You Can't Build a Subway Station, Right?

This show is about a mysterious cave in the woods. One of the characters disappears when they go inside the cave and is sort of this multiple plot line mystery. And it turns out that going into this cave, you enter a wormhole that can take you sort of backwards or forwards in time. So it's a sort of wormhole that has an opening at the same location on the earth, but different points in time.