Bishop's Castle is a long way from Durango, an eight-hour drive.
Previous respondents have mentioned Colorado National Monument and some have suggested that it's just so-so. You know if you want to see some pretty rock formations you could drive the Dolores River canyon from Uruvan to Gateway. It's a prettier drive and it's free. Both are a couple of hours from Durango, so they would not be on the top of my list for a vacation destination if my base was in Durango.
KC
Thanks for the correction, KC, I got this thread mixed up with the Colo Springs post.