The mine foreman, Garth, has the key to the gate leading down below the mines. The villagers are forbidden from going down there, but he'll let out-of-towners in if Lady Ekersfeld agrees and they really want. He will warn them that it's dangerous and try to change their minds, though. He will also let them know that he'll lock the gate behind them, so they should bang on the bars and yell if they need to get back out. The pit echoes loudly, so someone will hear them.
The villagers don't know what the symbol carved into the floor of the underground walkway is, only that it was made by the original builders. The fountain next to it was as well and does not work.