I have never heard of it before. Apparently it’s owned by the University of Michigan, and its future is uncertain:
The 9,900-square-foot, 22-room mansion was built by the founder of the village, Judge Samuel Dexter, a former U-M regent and noted abolitionist. Historians say slaves seeking freedom entered through a trap door on the veranda and hid in secret basement rooms.
Quakers delighted in the fact that Dexter and his wife, Millisent, entertained visitors on the veranda while slaves hid in the basement, according to Washtenaw County records.
At various times the Dexters also entertained Presidents James Polk and James Buchanan at their home.