This well preserved ghost town (like its near neighbour Bonanza) owes its existence to the discovery of gold and silver in the late 19th century and is accessible via a well maintained but unsurfaced road. Today, Custer City is the focal point of the the Land of the Yankee Fork Historic Area, and visitors can explore the remains of the town on guided and self-guided walking tours that take in cabins, stores, a schoolhouse (that also serves as the museum) and numerous other well preserved buildings.
If you go:
Custer City is open to the public for tours from 10am-5pm daily, Memorial Day thru Labor Day. From Stanley: Drive 11 miles east on Highway 75 to the Sunbeam Dam overlook. Turn left onto forest road #013 for about 9 miles. From Challis: Drive 42 miles west on Highway 75 to the Sunbeam Dam overlook. Turn right onto forest road #013 for about 9 miles.
Links:

Yankee Fork Road
Custer, Idaho 83278 USA
LAN@idpr.idaho.gov
Mailing address:
Land of the Yankee Fork State Park
HC 67, Box 2004
24424 Hwy 75
Challis ID 83226 USA
Phone Numbers:
Land of the Yankee Fork State Park
+1 (208) 879-5244
+1 (208) 879-5244