The trail to Lava Lake follows a very obvious route without any potentially confusing intersections, so unlike the vast majority of other hikes in this area, it is not absolutely essential to have a map.
After skirting above some summer cabins for the first third of a mile, the trail enters the Cascade Canyon, which it follows to Lava Lake. Total distance to the lake is just less than three miles, with an elevation gain of 1600. While not a stroll along the beach, this hike is very do-able for anyone in reasonable shape. The elevation is gained steadily and gradually, and a log bridge facilitates the only creek crossing of any consequence.
Views are somewhat limited for about the first half of the trip as the trail passes through a dense lodgepole forest, but open up as you get higher up into Cascade Creek. One other thing that could be viewed as good or bad, depending on your point of view, is that the trail is quite rocky. This is mostly a disadvantage for horse users, and the upside is that you wont encounter the mud bogs common to some other area trails with softer footing. Also, since the trail is not especially popular with horseback riders, hikers wont often have to step around horse droppings. As you start getting closer to the lake, the canyon bottom opens up with some meadows, a likely area to spot a moose. A little further and the trail switchbacks up the natural dam that backs up the lake, and youre there!
The views improve dramatically at the lake, with 10,412 Jumbo Mountain and several other un-named 10,000 peaks surrounding the Cascade Creek valley. Should you wish to make your trip an overnighter theres several good camping sites near the foot of the lake, and even day-hikers will want to spend some time savoring the rewards of their exertion. If youre interested in fishing, its worth wetting a line in pursuit of the resident trout, which are mostly in about the 10" range. Some of the lakes in the Spanish Peaks are noted for bigger (sometimes much bigger!) fish, but they tend to be considerably harder to reach than Lava Lake.
Although the official Cascade Creek trail ends at the foot of the lake, a well-trodden path extends to its upper end. Beyond that, you're on your own, though. Its not too hard to bushwhack about a half mile beyond the lake, but after that the valley becomes much steeper and choked with deadfall, making hiking beyond the lake a dubiously worthwhile venture. Seldom-visited Jumbo Lake and Cascade Lakes lie near the head of the valley, though, and I guarantee adventurous hikers will leave any crowds behind once they venture much beyond Lava Lake. Clearly, reaching these far off-trail gems will require or at least beg for an overnight trip.
For those wishing a longer trip, just before Lava Lake a trail branches off and heads up the ridge to the east, gaining a grueling 2000 vertical feet, mostly in the first mile, on its way to a high (9000) ridge. Once this ridge is attained, though, the going gets easier, and the views are tremendous. It eventually crosses Table Mountain and descends to Deer and Moon lakes after about eight miles. Then you can descend Deer Creek back down to the Gallatin River, from whence you will have to hitchhike back to your vehicle unless youve arranged a shuttle beforehand. Total distance between trailheads on the route described is about 16 miles. Obviously, only fit and experienced backpackers should undertake these sort of trips.