theres lots to do in old san juan, the shops and restaurants are wonderful, you must visit El Morro (the fort) very interesting and take note of the walled portions of old san juan. i believe you can get a walking guide to OSJ online either at frommers or fodors travel sites, i'm sure others have similar tours laid out, it's not a big area and is steeped in history, ie the pavers used in OSJ were once the ballast on a ship

"Travel is fatal to prejudice, bigotry and narrow-mindedness" - Mark Twain