Hmmm, no hiking. Well do try to visit Chinatown. I'm from Vancouver but left years ago. Pretty sure there are tours of Stanley Park. A trip up the Harbourview tower might be nice, as is Gastown (visit the aboriginal galleries/giftshops). Nice restaurants on Robson Street (and Chinatown too of course). Look into a boat tour - even taking the Seabus across the Harbour to the North Shore is pretty cool. The Anthropology museum at the University of British Columbia is a must! If you like the beach, English Bay or the Spanish Banks are great. There is Maritime Museum with the boat (St. Roch) that completed the Northwest Passage (in reverse) next to Planetarium, both in a nice park if that doesn't tickle your fancy.
Look at this site for more info:
http://www.tourismvancouver.com/
Yea I think I gave you too much info for a daytrip, sorry.