Ask The Corps: Polar Fortress

The BoLSCon Narrative Track has shifted and it looks like the Tyranid invasion of Macragge is going to replace Anphelion.  Of course I plan to build a Polar Fortress for the final battle!  While Dagobah was going to inspire my Anphelion, I am definitely not going to use Hoth for my Polar Fortress inspiration. Hoth was a temporary fortification cut into the ice while the fortresses on Macragge will have been in place for millennia.

Unfortunately, I haven't seen a lot of art on the Polar Fortress.  I like the look of the Forge World Imperial Fortress Walls (except for the Cinderella towers) and there is a great rock-fortress in the Black Templar's Codex.  We recently featured the Fortress of Eagles in a Field report, but there's not much else I've seen out there for large emplacements.

Got links?  Where are the big impressive Space Marine fortifications out there?