From the Walser village of Bosco Gurin, you follow the red-and-white waymarked path over alpine pastures and rock slabs to the Bann alp, before climbing over large boulders to reach the little lake.
The ascent to Lake Schwarz is no longer so steep: it probably owes its name (black) to its very dark colour. Flocks of sheep are a feature of this stony alpine area in summer. Continue through the scree to Lake Üssera before descending to the Üsser and Endra Staful alpine pastures.
The descent through the larch forest back to Bosco Gurin is again very steep. Back in Bosco Gurin (check the bus timetable from/to here in advance), why not visit the Walser Museum to learn more about the history of this enclave?