Lake Svartsjön is a nice lake with a right at the shore. Behind the shelter is a privy/outhouse, and 700m north of the shelter is a drinking water source. The shelter offers a fireplace, a couple of benches. There is a small and unstable jetty going into the water, but there is no ladder to help you get out. Beware that it is not super deep if you jump in from the jetty.
Note that if this shelter is occupied, it is only 2km to lake Nävsjön with numerous shelters on all sides of the lake. But lake Svartsjön is more remote and maybe more cozy.