Yes they can be very dangerous and the state has a program where they will fill in and block old mines on request.
This one is in the back of on old building in town that is now a coffee shop, you can take your lunch back there and sit in some of the carved out small rooms where they have tables set.

This one is just up the street from me and is fitted with heavy iron doors to keep kids and bears out, they are not all this developed though, mine is just a small tunnel 100 ft long in the side of a hill.