I enjoyed the Oregon Trail ruts (left by wagon train) near Guernsey Wyoming. Of course Yellowstone NP is always a pleasure for me. I’m fond of Estes Park in Colorado which has many trails and day hikes.
Thanks - YES, the Guernsey Rutts are amazing. Yellowstone definitely/ I travel with a geologist (!) so rocks are must-see. Have not been to Estes Park yet. Thanks.