You can also get there from Union Creek, Swift Creek or Big Flat trail head.
If you take Boulder Lake you'll have to cross Boulder Creek which can be very fast in the spring. After this you'll start the steep climb up 3,000 vertical feet to Foster Pass.
Along the way you'll get amazing views of Cub Wallow Meadows
and the East Fork Coffee Creek watershed. After awhile you'll see a trail junction sign. This is the turn off for Conway Lake. It's only a few hundred feet off the trail so be sure to stop and take a break at this beautiful mountain pond. There is no trail to Lion Lake but you can work you way up from Conway Lake without too much trouble.
If Lion Lake is not your main destination, you'll be best off passing it by, while still getting a truly awesome view of it from the trail.
Foster Lake is just on the other side. The trail is very steep, so take your time and be sure to stay on the trail. There are lots of spur trails that come off of the main trail above Conway Lake. Most of these try, but fail to reach Lion Lake which is protected by a two or three hundred foot cliff along its north shore.
Foster Lake has great camping if you can stand the wind that comes up out of Union Creek. If Foster Lake is crowed there are a few small off trail lakes that one could hide at.