Reger wrote the "Bocklin suite" for orchestra in 1913. Each of its four tone-poems is inspired by a painting by Bocklin ; Die TotenInsel (The Isle of the Dead) is the third part of the Suite. Bocklin painted not less than five versions of this picture beetween 1880 and 1886 (two of them are attached below). This picture inspired too the well-known tone-poem, with the same title, by Rachmaninov.
The work is a kind of a succession of small fragments, alternating soft ones and sudden and violent climaxes. As one could guess, the atmosphere (c sharp minor) is quite dark and gloomy, at least until
7:07 when a broad crescendo in D flat major brings some light and hope.
If you have the opportunity, the complete suite in its orchestral is more than worth listening and shows a very different Reger from what we hear in his organ pieces.
The transcription for organ is by Serge Ollive.