Not sure about the first one (if you're talking about the bit that I think you are then Tinuviel's right, pay the man the money and then go and tell the shopkeeper).
For the second, as far as I can recall, the entrance is a ladder towards the bottom of the screen. The area looks a little like a tire, yes (round, hole in the middle, don't know if you have Polo mints otherwise I'd have used that as the example). Well, along the bottom, but on the inner wall, roughly in the middle of that stretch of wall. Move your mouse about and the ladder will probably light up as you pass over it.
Of course, if we're really lucky someone like kiya will promptly put a screenshot up and my vague burblings will be just, well, vague burblings.