And the Untersberg, the nearest alp, viewed from just outside Salzburg (I've been up it, there is a cable-car that lifts you most of the way):
Haydn spent most of his career employed by the Esterhazy family who built a magnificent estate, a rival to Versailles but with more bathrooms and several concert halls, also in the countryside.
Beethoven was a nature-lover, who spent a great deal of time in walks in the countryside around Vienna. His Symphony No. 6, known as the "Pastoral", is one of the fruits of this time in the countryside. Here is the second movement, titled "Szene am Bach" (Scene at the brook).
Though born in the port city of Hamburg, Brahms moved to Vienna as a young man. He spent several summers at Lake Thun in Switzerland, during the last of which he composed the songs op 106 and 107 and the third violin sonata. Here is Lake Thun:
And of course, in 1893, Mahler, in what seems to be a developing pattern for composers at this time, acquired a retreat at Steinbach, on the banks of Lake Attersee in Upper Austria, and established a pattern that persisted for the rest of his life; summers were dedicated to composition, at Steinbach or its successor retreats. Here is his little composition hut:
I must admit that I have fantasized about something similar. When you are trying to compose, what you need above all else is solitude. And quiet. Nothing but the sound of little waves lapping, perhaps the occasional bird...