From Denver/Colorado Springs: I-25 S to CO-115 S.

Turn right on Third Street (due west) as you enter Penrose, which turns into Fremont CR 123 in about 5 miles. Observer Ranch will be on your right (north side). 

From Pueblo: I-25 N to Exit 101 (50 W) until you get to CR 67 and turn right (due north). Go approximately 3 miles, turn right (due east) onto Fremont CR 123, Observer Ranch will be on your left (4509 CR 123).