Rocky Mountain National Park charges a fee to enter. Fees are $25 per vehicle/motorcycle. If you are entering on foot, horse, or bike the fee is $15 per person. You can also purchase a park specific annual pass for $70.
Trail is fantastic. First part follows the Longs Peak Trail through the woods. Climb is consistent and gentle, very easy. It steepens a bit once you get past the tree line, especially in the stretch immediately before the outhouse at the trail junction. After the junction you go downhill for a bit, and then have to scramble up a ~150 rockfall to reach the lake. Take your time and follow the cairns.