The Mines of Moria
Don't worry - this beast to your right no longer dwells in the Mines of Moria. I still wouldn't reccomend it because it is incredibly difficult to enter and by no means OSHA approved. It smells and is super damp. While it is an incredible piece of history, it definately isn't worth your while to visit. DO NOT wander down random tunnels because you will not find your way back, and remember that any hand rails you do see probably aren't going to support you. Visiting is still doable as long as you stay in the main city of Khazad-Dûm and leave before you get tired of the smell.
Credit: HiddenVale