Limited by Time Constraints - A Day in Paris...

Unfortunately the best way to see any city is by not being trapped on a boat...especially Paris where you could spend months and still not see everything. My advice is to forget the Louvre and most all museums and stay outside on the go so that you can at least "see" a few sights as you go by. Lines at most all of the landmark tourist sights will be so long that you won't be able to waste your precious little time actually "waiting" to go up the Eiffel Tower or go to the top of the Arch. I just can't even imagine having only a few hours.

I walked the walk you describe. It was very disappointing. The monuments were great, but the Champs-Elysees was crowded with, well, other tourists, some of whom were not well-behaved. Lots of luxury car dealerships and very overpriced restaurants. Walk around the Ile de la Cite instead.

You can have a fun day and get a taste of Paris. Depending on the season you may have to plan for lines and would need to budget your time carefully. Determine what is most important to you.

Your planned walk is about 5 miles one way, how much time do you have? Investigate the buses and metro to shorten the walk and facilitate return to your cruise boat. If going up the Eiffel is a priority, book your tickets on line as soon as advance tickets go on sale. If you are there in the evening watch the tower twinkle at the top of the hour.

Plan time to sit in a cafe, eat croissants and pastries.

Enjoy the trip!

The only time I have felt like a tourist in Paris is when walking down the Champs-Elysées, so my advice is to skip that. With only a day, you don't want to waste time standing in lines. Many guide books have 1 or 2 day itineraries for visiting Paris - check out Rick's Pocket Paris Guide. I would get one along with a Street Wise map, and use them to prioritize your brief visit. Spending an hour on a Seine cruise isn't necessarily a bad idea, but I wouldn't spend the day on a hop-on-hop-off tour as it is very slow and time consuming.. I would concentrate my time on the area in and around the islands, and perhaps St. Germain, allowing time for a nice lunch where you can sit outside and enjoy world class people watching. If you want to go high to get a good view, and have the time, I recommend the Montparnasse Tower. It has a terrific view, including the Eiffel Tower, costs about 13€ and there is usually not a long line to wait in. What you want to do is spend the day savoring the Paris ambience rather than checking sights off a list. In that way, I can almost guarantee you will want to return when you can spend more time. Good luck.

Adding to the advice to skip the Champs Elysees walk -- but I love the river cruise for seeing the outside of famous buildings (and view of the Eiffel Tower.) Louvre IF you love museums, otherwise spend the time just "being in Paris." If I were to pick one museum, it would be the Orangerie for the Monet waterlilies rooms, which even comes with benches to sit while absorbing the paintings. Metro to Arc de Triomphe for the memorials at the bottom and the view from the top.

Instead of walking the Champs-Elysée, which I agree will be very disappointing, do Rick's Historic Paris Walk. You can find it in his France or Paris guidebooks, or can download it here (bottom of page): https://www.ricksteves.com/watch-read-listen/audio/audio-tours/paris

Note that it starts at Notre Dame, so you can do it right after.

I also agree that if you want to see specific pieces in the Louvre, do so; if you are just going because it's a "must see when in Paris," skip it and see other things.

L'OpenTour has these double-deck busses that run routes through central Paris and would be an easy way to see much of the city. The city bus #69 is a similar option (and cheaper). It will help you start thinking about your next visit!

I'll second a double decker bus tour (hop on hop off type) we just stayed on the bus upper deck and toured Paris. Got to see all the sights - where they are located - took tons of photos.
If you want to get off at a certain spot (Like the Arc de Triomphe - you can go to the top and just hop on the next bus that stops where you got off.) We got on the bus at Notre Dame (there are at least 3 or 4 different double decker bus companies) - we got on one called "The Big Bus"

In the evening I would recommend the 1 hour bateau boat trip along the Seine. We bought our tickets on the side of the river (down the steps) from the Eiffel Tower. We were there in winter and it was very cold - but we still bundled up and sat outside and enjoyed the Paris lights....

I'd be happy to give you some ideas, but I first need to know when you'll be there - time of year and day of the week matter. So Monday in mid-June is different from Thursday in late September and from Sunday in early April. Also, is Paris where the cruise begins? What time do you have to be on board? more details, please.

9am - Right Bank Walk
Invalides >> Pont Alexandre III >> Grand+Petit Palais >> Place de la Concorde >> loop thru Tuileries Gardens, possibly visiting the Orangerie >> Madeleine >> Opera

Metro Line 7 from Opera to Pont Neuf

12pm - Seine River Cruise
1 hour cruise with Vedettes du Pont Neuf http://www.vedettesdupontneuf.com/
(Get a great view of the Eiffel Tower whilst on this cruise)

1pm - The Louvre

5pm - Notre Dame

Metro Line 1 from Hotel de Ville to Etoile

7pm - Arc de Triomphe

Take in the beauty and ambiance of Paris by walking around the Ile de Cite, take the sightseeing bus, walk around the eiffel tower, have a nice meal in an outside cafe. And then go back another time and really see Paris!

I am assuming the Seine river cruise is not the local one hour thing but a longer cruise from which this is a break.

I agree that the Champs is a big disappointment consider walking through the Tuilleries from the Louvre (whether you go in or not) and then through Concord to the base of the Champs and walk up to the Grand Palais and then across Pont Alexandre -- this is a beautiful walk with great Eiffel Tower views.

If you go to the Louvre use the Carrousel entrance and hope for a short security line; if you have a ticket ahead you can use the bypass line to the right and sort of go to the head of the security line. Whether the Louvre is worth your time is up to you; we all have different priorities. Do the things that are your dream of Paris.

I agree with everyone saying to skip the Champs-Elysees. Here is what I would do based on what you've said:

Visit the Louvre first thing in the morning when it opens at 9; if you're major art buffs I imagine you could spend half the day in there, but assuming you want to keep moving, I'd try to head out by 10:30 or 11
Head over to Notre Dame and check it out from the outside (the line to go up is always really long, it always takes at least an hour and often more, so I'd only try to go up if you nixed the Louvre and got to Notre Dame very early, like 7:30 or 8:00 AM so as not to spend much of your day in line)
Follow Rick's historic Paris walk--I forget if that walk takes you to Ile St. Louis, but if not, I'd have a quick wander there (it's right by Notre Dame) first before starting the walk
At some point during the walk you may need to stop for lunch; the St. Germain area near where the walk takes you is a good place to find a nice cafe where you can have a leisurely meal
After the walk, do a little window shopping in St. Germain
Then head up to le Jardin du Luxembourg to relax with the Parisians; see if you can find a good game of boules to observe

Will you be in Paris for the evening too? I agree with those posters who said that the Eiffel Tower is best at night when all lit up. La Fontaine de Mars is a nearby restaurant with fantastic traditional food and atmosphere.

Finally, if you aren't absolutely set on the Louvre, may I suggest the Musee Rodin as an alternative that isn't quite so expansive and is easier to enjoy in a shorter period of time? Especially if it's a nice day out, exploring the sculptures in the gardens is wonderful.

I hope you enjoy your day in Paris! Any amount of time in Paris is worthwhile.