Warthur
At least one blogger refers to this stuff as "Winter Synth" - by analogy to the Dungeon Synth works produced by artists such as Mortiis (during Era I) and Wongraven - a comparison which is rather apt. The material is somewhat analagous to Dungeon Synth stuff since in both cases you are dealing with a musician with a background in black metal (not that all dungeon synth artists are black metallers, but the first wave generally were) dipping into dark ambient material produced on electronic instruments, but there's also stylistic differences. Dungeon synth stuff, for instance, tends to want to try and establish a quasi-medieval atmosphere and mimic medieval instrumentation, and doesn't show much influence from the wider world of ambient music.
Conversely, on Die Festung Paysage d'Hiver show the influence of electronic predecessors such as Klaus Schulze or early Tangerine Dream. The synthesisers are not afraid to sound like synthesisers here, but they're still channelled towards evoking a particular wintery atmosphere. Cold, almost unearthly - like a familiar landscape transformed by a fall of snow - the album is a fine piece of atmospheric background music.