Why did the travelers go into the cave in chapter 4: Over Hill and Under Hill?
They are trevelling up the Misty Mountains and are trying to find their way. Gandalf, Biblo and the dwarves go into the cave to get out of a terrible thunderstorm storm. Kili and Fili are sent in to make sure the cave is secure and they report back that it is. The cave is indeed cozy and dry, and seemingly empty. They lay out their wet clothes and take the supplies off of the ponies. What they don't know, though, is that the cave is actually and entrance for the goblins.