Challenging but incredibly enjoyable and fast route, would recommend to the first-time-FKTer in a heartbeat. Experience alpine lakes, pine forests, mountain vistas, and boulder fields in one short loop. See course description for the general route, see below for my experience. I'm really looking forward to the next true Colorado local or pro to tackle this one. If you only get one day in RMNP, do this run & do the park drive!
Protip: During COVID, Rocky Mountain National Park has a TIMED RESERVATION ENTRY SYSTEM due to popularity. Reservations-to-enter are mandatory between 6am-5pm everyday. Arrive before 6am to pass this system AND watch the elk herds in the morning. =) Start early to avoid the hiking crowds esp at Bear Lake & Fern Lake.
My experience: Started route at appx 8:00am after watching elk bucks clash antlers in the nearby meadows. Started route from Fern Lake TH and went clockwise, so that first lake hit was Cub Lake and to get the jeep road done first. Mid September seems the perfect month for this- no snow on trail, but just enough snow along the timberline area at Lake Helene to be picturesque. No crampons and no hiking poles needed.
The first push from Cub-to-Bierstadt-to-Bear Lakes is a tough uphill grind of never ending 5% grade- just shallow enough to run but just steep enough to fatigue. Moose was reported at Cub. Bierstadt & Bear lakes were small enough that I did a victory lap tour around. Terrain is mostly trails through meadows, skag forest, and pine forest. Bear Lake TH is a possible exit/resupply.
The second push to Lake Helene takes you from pine forest up to boulder fields and finally snow touched alpine. Lake Helene sits at the base of two mountains and is spectacular. Helene's turnoff is unmarked, check your map and don't miss it. If you hit the steep downhill you went too far, it's basically at the route high point. You really feel out in the wild here.
The third push is a long technical downhill route to visit Lake Odessa and Fern Lake. Don't miss the hairpin turn for Odessa- you'll run parallel to a very cool mountain stream. Watch for hikers as you blast downhill, especially after Fern Lake.
To see the Lakes: Cub Lake can be seen from trail, Bierstadt Lake needs sidetrip, Bear Lake needs sidetrip & down/uphill, Lake Helene needs sidetrip on unmarked trail, Odessa sidetrip along river path, Fern Lake can be seen from trail.