Let’s start off by mentioning that the Gem Lake trail from the Lumpy Ridge trailhead is free. There is no national park fee even though it is located in the Rocky Mountain National Park. This hike is considered moderate. It took about 3 hours for us to complete it, though we did spend some time making friends with the local chipmunks and took several snack and water breaks. We are more like amateur hikers in case you wondered. I just happen to be fitter with an addiction to cardio.
The Lily Mountain trail is also free since it is located in the Roosevelt National Park. Yes, you can take a dog with you. I would not deem it rational to drag along any animal other than one that is at least medium size and fit. This particular hike is considered moderate, but it is definitely challenging. I believe it took us 4 hours to complete.
The Gem Lake trail was okay, but I prefer Lily Mountain. Even though there was the small Gem Lake (more like a pond) at the end, Lily Mountain was more strenuous and exciting. I am glad my husband decided to force me to climb the large rocks to the left (the right is higher up). It made the finale of the hike worth it. So, yes, I recommend a bit of mountaineering if you have the courage to do so. I believe it made a difference.