Rocky Mountain National Park offers so many hiking options for all abilities and interests that it can be difficult to choose one. The Loch Vale comes very highly recommended. Less crowded than the hike to Dream Lake, it is nonetheless a busy and popular trail. Take the free shuttle to the Glacier Gorge Trailhead, as parking is limited.
The first part of the hike up to Alberta Falls is the most crowded, and after viewing the falls (which are far prettier and more photogenic from the river level than from the overlook), the climb higher is a bit less congested. Be on the lookout for elk near the trail in this area. It is a steady climb winding up around Glacier Knobs above the falls, then a nice stroll down the little valley with increasingly grand views of the surrounding cliffs and the high peaks beyond. The last climb up to the lake level is another steady climb up the side of a narrow canyon.
At last the lake is reached, and it is a real beauty. There are many wonderful ledges and rocks to use for lunch or fishing, and the trail wanders along the north side of the lake with lots of social trails to the shore. The view of the 12,630-foot Sharkstooth peaks complex is spectacular.
The 4.5-mile round-trip hike to The Loch may be enough, but energetic hikers can continue another mile to Timberline Falls (which can be distantly seen from The Lock outlet), and a fairly steep climb further up to Glass Lake and Sky Pond.