must see attractions in London

I wouldn’t recommend the HoHo bus - take regular buses and sit upstairs at the front to see the sights.

Museum - I have enjoyed the London Transport Museum more than any other. My second choice would be the V&A.

Church - Westminster Abbey

Palace - the former palace of the Tower of London.

Other sight - the Houses of Parliament.

The hop on hop off bus is a waste of time and money. Traffic in London is abysmal.

Visit Parliament Square on foot. ( Parliament, Westminster Abbey). From there follow Birdcage Walk adjacent to St James park up to the Palace. Changing of the Guard not worth it. Instead check this website for the https://changing-guard.com/household-cavalry.html
Far less crowded.

Also if there is any interest in the Churchill War Rooms pre book timed entry tickets. I visited nearly 8 years ago. Well done and throughly enjoyed seeing it.

One church: Westminster Abbey. ( take the Vergers Tour ) One Palace ( walk by Buckingham but tour Hampton Court Palace. Train from Waterloo ) One Museum: Water and Steam or V and A…the latter only to have tea and cake in the V & A cafe. As an actual museum to wander about: The Horniman Museum or Wallace Collection or Sir John Sloane Museum. I also liked the Imperial War Museum.

Don’t miss the Tower of London. Then walk towards the Gherkin and visit the adjacent Leadenhall Market. Last glass covered market in London.

Personally I’d also not miss Spitalfields Market. Lots to meander about. As I travel in November its always my stop for one of a kind Christmas cards and ornaments. Ages ago my friends and agreed no Christmas gifts…ornament exchange.

Lastly, www.walks.com are inexpensive and well done. Small groups, stellar guides. I’ve taken one on each visit. Most recent was Inns of The Court in July. Over the years have enjoyed Jack The Ripper, Old Westminster by Gaslight and Victorian London tours.

For Museums, it really comes down to where your interests lie. There really is an embarrassment of riches to choose from depending if you like ancient history (British Museum), Victorian era (Victoria and Albert), Art (National Gallery, or the Tate if your tastes go modern), Military (Imperial War Museum, Churchill War Rooms, HMS Belfast), and then a whole host of smaller museums with specific interests.

A big no to the hop on hop off bus.

I know that you need to keep walking/steps within a reasonable amount.

One idea: Start at the Tower of London right when it opens. See the Crown Jewels first and then wander around. Don’t try to do the White Tower, it has hundreds of stairs. Walk outside to the Tower Pier and take an Uber riverboat to Greenwich. This gives you a nice rest sitting down and an interesting perspective on London from the Thames. At Greenwich eat lunch and decide how far you want to walk. The Cutty Sark Clipper ship is right there and has elevator access. A little further from the dock is a good naval museum.
Take the Uber Boat back to the Westminster Pier (another good rest) and then see Westminster Abbey by doing a verger tour. This will be a full day. If energy you can add more in, but this will give you key sites and good rests between them.

For the best museum advice you really need to decide whether you want art (what period?), decorative art (that would be the V&A), history (what period?) or something else. Unfortunately for short-term visitors, many of London's museums are massively large; it takes multiple days to see each one. You don't have that much time, so I'd recommend either choosing smaller options than the British Museum/National Gallery/Tate Modern/V&A/Imperial War Museum or taking a look at the website to zero in one section of the exhibition that's most of interest to you. All the museums I've listed there are free/donation-requested, so from the financial perspective you don't have to worry about spending a lot of money for a partial visit.

The Churchill War Rooms take over half a day for a full visit if you want to take in all of the Churchill Museum section.

Also be aware that London is a very large city. You could easily spend close to two hours a day just moving from sight to sight on buses or the Underground. I'd depend on a map to help me pare down my target list.

This is such a personal decision and my interests might not align with yours.

Museum - I'd go to the British Museum but I like that kind of museum and you might prefer an art museum. My favorite art museum is the National Gallery.

Church - Westminster Abbey but I like the history behind it and love to search out who's buried here.

Palace - Honestly, on a very short 1st trip I might skip a palace in favor of another sight...but this is purely up to you

Other sight - Agree with the others that Tower of London is wonderful. I also love the Churchill War Rooms but if you don't have an interest in WWII history this might not be for you. I'd do the War Rooms before one of the palaces in London but I have a strong interest and you might not.

I think you were also going to get Rick's London guide? I'd also read thru his list of sights and see what appeals to you.

One museum - Churchill War Rooms

One church - Westminster Abbey

One palace - Windsor Castle

One site - Tower of London

Those were our favorites and the ones that we still remember the most. You can easily take the Tube or train to most locations.

One museum - either V&A or Kensington Palace

One church - St Pauls Cathedral

One palace - Hampton Court Palace

One site - Tower of London

oh and edited 'cause I forgot - nix the HoHo

As others have said, it’s really down to your interests. But since you asked, here were my priority choices for a three day London stop, my first time being there:

Museum- British Museum.

Church- Westminster Abbey

Palace- Meh. See a play instead. (Because it’s about your interests and I didn’t care about palaces)

Site- Boat tour of the Thames. I didn’t actually do this but think it would have been a nice addition. I did walk along the river and took a Uber bus back up, but a tour would be interesting.

I managed to fit in some other things, the RS Westminster walk us nice to Trafalger, but London is a big city and it takes time to get from place to place even if you stay within central London. And allowing time for a pub lunch or tea, if that’s of interest, will take up even more of the daytime sightseeing time. I’d pick one important thing per day based on your priorities, and then walk around to see whatever else is reasonably nearby to fill in the time. A play or nighttime boat tour or maybe Trafalger Square at night can fill up the evening if you don’t need sleep or rest.

Attraction- Tower of London

Museum-British Museum or Museum of London

Honestly-unless you are into royalty, I'd take a miss.

I love markets so I'd either go a Borough Market or another London Market close by

Also go to Londonwalks.com and pick a neighborhood walking tour. Some of my fondest memories of London on the pub tours.

• I was going to mention the Museum of London as well but it is closing
  in December for a couple of years as it moves to a new location.

• I'm going to count the Tower of London as a museum as it does have some outstanding exhibits, my favourite is the armour in the actual tower.

• Hampton Court Palace was one of Henry the VIII's homes and is
  outstanding.

• For a church I'd go with Westminster Abbey and consider seeing it via
  a tour with London Walks.

• My other is to consider Leadenhall Market and dinner at La Vina.

Here's Rick's list:
https://www.ricksteves.com/europe/england/london-itinerary
It's for 7 days, and I know you don't have 7 days, but take a look anyway to see what appeals to you.

If I had to pick.....one museum:
Victoria and Albert Museum, the V&A.
Tie with: The British Museum.

One church: Westminster Abbey
Be careful of the steps. In many places, there are one or two steps up or down. The interior is somewhat dark, so look down occasionally and be careful. It would be easy to fall on those stone steps.

One palace: Hampton Court Palace.

One other sight: The Tower of London.
Even if you only walk around the outside of it and get a good look (without paying to go in). There are steep stairs inside the round stone turrets and long flights of wooden stairs inside the White Tower. I don't know if you'd get your money's worth paying to go inside, considering the difficulties of these stairs.
I'm also thinking of the bone and foot problems you've told us you have, so not certain these stairs would be safe for you.
My mother had the same bone & foot problems and could not have enjoyed climbing the stairs here.

Westminster Abbey, Tower of London, Hampton Court Palace, British Museum.

Thank you all for your suggestions.

I am planning to buy Rick's book on Black Friday from Amazon.

I love museums -- really love them. And I love all kinds of museums. Realistically, I am possibly going to be able to visit two but may have to limit what exhibits or rooms I am going to visit. I have visited some of the websites and am very impressed that some are free but I have also seen that some are huge and I mean huge.

But I also must see at least one palace and one church as well as one other sight.

Trite but true-British Museum, Westminster Abbey, Tower of London.
One other site-I would do the expensive tea or ice cream at Fortnum and Mason. Or if you like art, the National Gallery, which is walking distance from F&M. EDITED: or if you loved the British Museum, but ran out of energy, go back there. I think admission is free.
If you had an entire day and good weather, my choice would be Kew Gardens, taking the boat from Westminster Pier to get there. It is a lot of walking. There is a small palace there, but I wasn't very impresssed.

In my opinion, the Changing of the Guard would be a definite no.

Top tip for visiting London if you can’t walk too far is to use the buses rather than the Tube. Citymapper app is your friend. You’ll spend more time sitting and less time on your feet.

Well, kudos for recognizing your limitations up front and bring realistic. I’ll warn you though that London is one of those places where you can be tempted to push those boundaries, there’s so much to see! I’ll break from your question a bit and maybe suggest things to leave out.

I did not care for the hop-on-off bus at all. You spend a lot of time in traffic on pretty uninteresting streets, stopping occasionally for a few minutes more to pickup/drop off people. It actually made me more tired.

Skip anything that’s an outlier/time-consumer: any palace, the Eye, the Tate, Tower bridge (you’re just going to take the same picture everyone else is.)

Must sees that deserve your attention and energy? The British Museum’s Egyptian wing, and the Elgin Marbles, along with whatever else you can manage before your brain falls out. Westminster Abbey is a must, but not especially taxing. I’d put St. Paul’s on the same level honestly. Churchill War Rooms and museum is excellent and unique, but wore me out a bit. The National Gallery may be open late while you’re there. If you’re not sure you can do it, maybe just reserve a ticket and see how you feel.

Taxis can also be key. Trading 30 minutes of walking/tube versus a carefree return to your hotel to recharge can make a massive difference.

It is going to be VERY difficult to make decisions about what to see and what to pass on. I have been watching youtube videos and I feel like I must add on another day or two but I am not.

I can only give so much time and spend so much money.

I am going to have to make some difficult decisions when it comes to London but I think that I will love whatever I can see and do.

I did buy Ricks' book and it is arriving Wednesday.

Thanks to all for their help.

We found the hop on hop off bus not worth the time or money. You spend more time in traffic than anything else. We walked everywhere. Or took the tube.

After spending a week in London, these are the places I found the most interesting:
1) Churchill War Rooms ( audio tour is excellent)
2) Westminster Abbey (a 5 minute walk from the Churchill War Rooms)
3) Either the National Portrait Gallery or The Victoria and Albert Museum
4) Saint Paul's Cathedral