what can I do in Nice in one day?

Yes, defintely Fenocchio's. How could I forget? Thanks, Roe.

You can visit a museum (Chagall, Matisse), stroll the Promenade des Anglais, explore old Nice and the Cours Saleya.

Take the bus up to Eze Village.

I agree with Grier on this one. I would add getting gelato at Fenocchio's in the Place Rosetti. You won't believe how good it is, or the range of flavors.

1. Go to the old market area 2. Ride the streetcar down the main street 3. Walk along the beach 4. Visit the museums noted by others. 5. Visit the gardens - lovely and peaceful

And eat a wood-oven baked pizza at La Pizza on the pedestrian street, rue Messina.

When we were there in June we only had one day also. We walked on the promenade down to the elevator that takes you up to the top of Castle Hill. Ride the elevator up for great views along the coast and an overview of Nice. We really liked this a lot. Of course we also went to the old town market (Cours Saleya) and tried the Socca and did some shopping. My wife enjoyed the walk through the old part of town. We also took the tram ride through modern Nice (had to go the train station anyhow) and that was worth the time.

The Russian Orthodox cathedral is about a 10-minute walk from the train station. Beautiful.