In You Go!

You yank on the rusty grate until it gives up and bends open. Thanks to the shady lighting in the canyon, it doesn't take long for your eyes to adjust to the dark inside the cave. The air is noticeably more still. You are standing in a forked hallway, with two directions you could proceed. The room is not quite level, so the left passage slopes gently uphill and the right-hand passage slopes gently down.