I am going to be in Oslo on a cruise and would like advise as the best sights to see in one day.

Here are just a few that I highly recommend in the following order:

1. The Kon-Tiki Museum at Bygdoy.
3. The castle/fortress down by the seaport area - great WWII museum in there about the resistance.
3. Frogner Park - Lots of sculptures.
4. If you have time, you might want to visit Holmenkolmen, site of the Olymmpics back in the 50/60's. Great views.

Frogner Park is a must. I am not into the arts, but the park and statues are very unique and certaily worth the time spent.

Thank you for the info.

If you do like art I would also recommend the Munch Museum devoted to the work of Edward Munch.

Also if you are going to the Kon-Tiki Museum which is fun nearby are other nautical museums devoted to restored Viking ships (small but very impressive)and polar exploration.

Bygdyy is worth at least half a day and I think the best museum of all is the outdoor Norsk Folkemuseum. [http://www.norskfolke.museum.no/]
The Frognerpark is also unique. See
http://www.planetware.com/photos/PHN.HTM for photos of both.

"The castle/fortress down by the seaport area - great WWII museum in there about the resistance."

Akershus Festning.

Cruise ships dock at the feet of Akershus Fortress. Sightseeing buses always are seen in the area, meaning that your captain for sure will know how to join the different sightseeing options, wether specifically to Bygdoy, the Vigeland Sculpture park, Holmenkollen Ski Jump or all of them. Tours vay, I guess from 1-2 hours overviews to whole day excursions with inside visits to the main attractions.

However, if nice weather and being in relatively good shape for walking (3-5 miles during the day), I certainly would prefer a self-guided Akershus/City walk combined with a ferry (10minutes) to Bygdoy and the museums out there. Maybe also combined with the Vigeland Sculpture park.

Akershus Fortress is a very nice walk, and from the top of its walls the Oslo and the Fjord sights are excellent. Except, of course, for the part that might be shadowed by your cruise ship. Allow a small hour or such.

Then head for Karl Johan Street and the Parliament. 5-10mins from the Fortress. Follow the street (on the park side) from the Parliament and westwards. Grand Hotel on your right, then lots of bookstores, music and souvenir etc also on the right. A big statue of our famous poet Wergeland in the middle of the park, and then the National Theatre, with Henrik Ibsen and Bjornstierne Bjornson statues in front. Forther, to the rigth, the old University buildings, and behind that (up Universitestsgaten - University street) you'll find the National Gallery (entrance free). Munch's famous "Scream" is located there, by example.
Then on the end of Karl Johan, the Royal Castle. Might be worthwhile to get close if the Guard's changing is on.
Anyway, when having passed the National theatre, you have two options:
1) Go by the subway - T-bane (western) one stop to Majorstuen, and walk your way south to the Vigeland Park. Some 500 meters. Ask for directions. Most people gladly will help you. Enjoy the park, do not forget to get to its highest point with the "Monolite" sculpture. Very nice views. Refreshments at the cafes close to the bridge. Return the same way you arrived, or continue straight south to Bygdoy Alley via Noble's street. Here you'll pass US Ambassy's reseidence to your right. In Bygdoy alle there is a bus stop, and route no 30 will take you directly to the Bygdoy Museums. Nice ride.

Day-cards for public transport is recommended. NOK 50 per adult, purchased at your firs enter. Works for the sub, buses, trams and ferries.

2) Head for the Harbor through Olav V's street. A great handicraft shop, Norway Design, is the first shop on yor right when you cross the tram line at the western side of National Theatre. On your left, then, is Hotel Continental with the great Art-Nouveaux/Jugend restaurant The Theatre Cafe!! Expensive, but still a lunceon top notch.
Close to the harbour you'll have the City Hall to your left, and the Museum Ferries right in front. A big white sign wit the text can not be missed by your eyes. It takes you in 7-10 minutes to Bygdoy. If the Viking Ship and/or the open air Folkemuseum is of interest, leave the ferry at first stop and walk the 5-600 meters up Huk Avenue to reach the museus. From there follow signs to "Fram" "Kon-Tiki" to get to the polar ship museum area where also Kon-Tiki is located. Or take a shuttle bus Museum
Return

Sorry. Computer interruption. Here's the continuation of the selfguided sightseeing story:

The Viking Ship - Kon-Tiki Stroll is about 1 kilometre, perhaps 1.5.

If you do the option 1), Vigeland Park and then bus 30 to Bygdoy, the bus stops both at Viking Ships and at Kon-Tiki. Meaning that option 1 and 2 join right here.

If only Kon-Tiki and the Polar ships are of interest or within time limit, and you go by the ferry, do not leave the ferry until second stop, whhich is right in front of the museums. By bus go to it's end stop.

Enjoy, and get back to town and your cruise ship by the ferry. If caring for a refreshment at some more moderate prices than Aker Brygge, choose "Ferja", an old wooden ferry turned into an outdoor cafe. It is located in the Akershus Fortess corner of the harbour, where you'll have to take to the right to get to your ship.

Bjorn, Oslo

To add to the good advice, Oslo is very walkable. Allow time to eat at a harbor side restaurant. the seafood is fabulous and a great way to catch your breath and people watch. Can't wait to return in July...just to eat!!!