Snakes. Why did it have to be snakes? Thanks to a combination of my physical prowess, ingenuity and carefully applied pressure (in other words, I tripped and fell against the button) this secret door opened. I couldn't see much inside, but I could hear this kind of reptilian slithering. Ever since that adder bit me, I've never liked those things.
But right now, it looks like whatever we do will have to be done by the others, because there is NO WAY I am setting one foot inside that room!