Old Lexington Stamp Mill and Gardens is located in Butte, Montana. The stamp mill was built in 1867. It's not a stamp mill that makes postage stamps. It's an ore-crushing machine that pounds rock into fine sand. A lovely botanical garden has been developed around it. One of the features is a botanical butterfly, which is a replica of one from an amusement park which had closed down. It's a rather pretty feature which can be seen from the road as you drive by.
The gardens are open May through October from dawn to dusk. Admission is free.