What to do in a single day in Edinburgh

Download Rick Steves app on your phone and click on My Playlist > Britain Beyond London > Edinburgh: Royal Mile and take this easy self-guided walking tour of the main drag. If you like whiskey, there are tours you can take afterwards.
Another adventure is to walk up Arthur’s Seat. A walk around the botanical gardens is the most beautiful walk I’ve taken but you should invest in Rick Steves Edinburgh guidebook that dedicates a whole chapter to this jaw-dropping self-guided walk. A 4th edition of his book comes out in Feb.
If the weather is good spend the day outdoors. If it rains tour the Royal Yacht Britannia.

Many years ago, during a spring break trip with a friend, we took a very early morning train from London to spend a day in Edinburgh. Coldest I’ve been in my life, but one of the most memorable day trips in a lifetime of traveling.

We toured the Castle, walked the Royal Mile, went into shops and chatted with the shop keepers, bought sweaters to add to the layers we were wearing, and stumbled upon a Scotch tasting.

We had nothing planned, and probably 7 hours in the city. I still remember turning a corner to get out of the wind, and found a wonderful restaurant for fresh salmon from the Scottish waters.

Whenever we travel together now, we talk about what a fun day we spent in Edinburgh.

I plan to travel there again in a couple of years, and will want to go to the Palace of Holyroodhouse and tour the Queen’s Gallery art collection.

Whatever you plan to do, or just wing it, I hope you have memorable experiences.

Tour the Royal Yacht. We thought it was fantastic piece of history and besides you get to see the Queens bedroom! Also enjoyed Mary Kings Close just down the street from the castle. Have been there twice and would go again. You get to see underground Edinburgh. Walk by the churchyard to see the statue to Greyfriars Bobby. Not too sure how true the story is but I like to think it is. It's just down from the castle also. Don't eat at the restaurant there it is mediocre at best in my opinion. Try to be looking at or near the castle at one o'clock when they fire off the cannon to announce the time. You can also.stop in St..Giles for a quick look at the church. Just a few suggestions. Enjoy .It is a truly beautiful.city.

I don’t think you need to invest in a book for just 12 hours. You obviously can’t see everything so you will need to prioritize what interests you the most. Online research can help with that. Castle tickets are timed entry. We’ve been before and we are going again with friends next month. We’re going when it opens so there will be less people. The castle and the Royal Mile pair nicely.

Just start at the castle at the top of the hill, tour that, and then make your way down the hill to Holyrood house at the bottom and tour that. Between the two there are plenty of shops, St. Giles cathedral, and some other museums, closes, and architecture of interest. This could take you five or six hours at a moderate pace if you were to spend an hour and a half at both the castle and Holyrood, and spend a couple hours at places between. You would still have time to walk around the base of the castle, or walk up Carlton hill after Holyrood and get a great view of the city. You might also visit the Walter Scott monument which you can also climb, and there is the art gallery and park near as well. I also toured a Georgian manor house that was quite interesting. This is a good map: https://www.introducingedinburgh.com/map/royal-mile

If you're unlucky with the weather, the National Museum of Scotland is a good choice--a modern museum with a wide variety of exhibits very attractively displayed. There are also multiple good art galleries.

Rick's top sightseeing suggestions are available on this website. Choose Explore Europe > Scotland > Edinburgh > At a Glance.

If the timing works, try the Royal Mile tour with Mercat Tours. We did it in June and it was very well done. So much information that you won't get by walking the Mile yourself.

https://www.mercattours.com/view-tour/secrets-of-edinburghs-royal-mile

I would start at the castle, which you can tour or not depending on your interests. Then walk down the Royal Mile stopping at whatever places strike your fancy. I enjoyed St. Mary's Close. Go all the way to Holyrood Palace, which I don't think is worth touring on a short trip. Then head over to Arthur's Seat, which is very fun to climb; the views are terrific. If you still have time, wander over to Princes Street -- the view up to the castle is pretty great -- and new town.

Just added a note but if your cruise ship docks near the Royal Yacht I would tour that first thing then take bus to Old Town.

Hey - I wanted to take a moment on this forum to THANK you all very much for your advice and tips. Edinburgh was fascinating. We were anchored off shore, and had to use ship tenders to get ashore. Once ashore, I chatted with a local, who recommended I take the local city bus -which I did. Gave me a look at everyday Scots. Not the touristy guy dressed in full costume playing bagpipes, or some guy with face painted half-blue waving a sword around recreating Braveheart. So, many thanks. I very much appreciate your advice and tips.

Holyrood Palace, Royal Mile, St. Giles, and the castle would take up most of your time. Nothing wrong with the other suggestions.