According to his wife Alma's journals, Mahler's life there "was stripped of all dross, almost inhuman in its purity".
He woke at 6:00 or 6:30 A.M. and immediately rang for the cook to prepare his breakfast: freshly ground coffee, milk, diet bread, butter, and jam, which the cook carried to Mahler's composing hut.
With his coffee (and warmed milk), Mahler would work until midday, and then go into the lake for a swim with his wife.
After a light lunch, Gustav would take Alma on a 3-4 hour walk along the lake shore, occasionally stopping to jot down ideas in his notebook. These composing breaks would sometimes last for an hour or longer.
Extraordinary that with only a few months each summer, he was able to write so many seminal pieces of music. All this, I suppose, is partly thanks to his ability to leave the noise behind and focus on the few things that were truly important to him.
Here's the interior of his hut. Nothing but a piano and some beautiful views...