Running through forests is good... running through forests to get to amazing views of mountains and high alpine lakes, is great. Even better is climbing those mountains and seeing yet more mountains... Mountain running is fun!
There is water from streams and from the lake that can be purified if you want. Some people may choose to backpack into Crater Lake and explore from there as a trail running trip.
This run begins at Andrews Lake just south of Molas Pass on the Crater Lake Trail #623
. This whole trail is highly used to Crater Lake, so there is no doubt what trail you should be on. The trail to Crater Lake is just under 5.5 miles, but it just seems to be longer, I don't know why, it just has that feeling to me.
Take several switchbacks and gain some elevation before you make your first meadow. You'll seem to repeat yourself as you climb a "step", go into a meadow, and go back into the forest.
At about mile 4.5, you'll come to a large area with many downed trees due to a microburst. During the run, if you have forgotten mileage, know this, that once at the downed trees, you are close to the lake.
Run a little further and come to the first pond below Crater Lake. Continue just a little further, and you'll arrive at beautiful Crater Lake.
If you have arrived at Crater Lake and decide that, that wasn't enough... good! There are quite a few social trails and campsite trails to explore, and if you just stick to the lake for a quarter of a mile, you can then start making your way up the slope. My wife and I didn't really stick to any trail here just went up the path of least resistance until you get to an open meadow.
As you look up towards North Twilight, you should be looking at its north face. Make your way toward runner's right of the north face where you'll see a faint trail. The trail will take you along the ridge and then out onto the face. Again, this is a very steep trail so take the path of least resistance. The path marked on this route is only my interpretation of what the easiest route up is.
When you top out on the face, scramble/run the ridge to the top of North Twilight for yet more amazing views of the San Juans. Make your way back along the same route and back to Andrews Lake to complete the run.