In the time of Sauron, when he waged war on Middle Earth, the biggest loses came to the dwarves. Mines were overrun by orcs, warriors killed in battle, and glory came to none.
But not all loses were caused by Sauron. Some, like Moria, were caused by greed, by ancient powers that consume, destroy, and take over the actual powers of Middle Earth. Demons, from the very depths of hell may come to haunt the living, if they are disturbed.
After the defeat of Sauron, the dwarves had to rebuild what was lost, and the easiest way to do that is to reconquer had once been theirs. Now that the dwarves know of the dangers inside, they go, with Gimli in the first lines, to retake Moria.
This will probably be stat-based, but it might just go as it is. Also note that this will be the first time I GM. I'll post a CS skeleton if I see interest.