You can explore the city, but you have to be careful of the floors you can fall through. The only way to explore LC is to use the cheat where you jump 5 times as high, or something like that, over the wall in the yard where you kill the remaining thugs - you might need to use the nearby car in the yard as a platform. You'll land in a back alley in Saint Marks, walk to either end and stop before the main road. You'll then need either Infinite Ammo cheat, or thousands of bullets for one of your guns. Shoot the ground ahead of you to see if you can walk on it, if sparks appear you can walk on it, if there aren't any sparks when you shoot, then you'll fall through the floor if you walk on that area. Using this method, you can reach your safehouse from GTA 3, you can see the hospital as well, but not much more than that. It's nice they made the effort to make some of LC again.