Mt. Useful

 is a limited-time premium building that was released on December 8, 2021, during Act 1 of the Holiday Whodunnit 2021 Event. Upon completion, Park Ranger is unlocked.

Trivia

 * Only one can be obtained.
 * It can be placed on grass, pavement, dirt, krustyland road, boardwalk, pier, edge of boardwalk, or edge of pier.