I found that I wasn’t using one of my favourites among my own mods – Markarth Dwemer Palace – because it was inconvenient to get to and because I forgot it was there. Having some sort of exterior, even a very small one, resolves that. This new “portal deck” area leads to/from the elevator entrance and is located right next to Markarth Stables.
Skyrim Nexus gives a choice of files to download: the regular one requires the player to battle the lich in the dungeon, then pull the lever to enable the exterior (which is otherwise invisible). The alternative version has the exterior part visible all along. (In my mind, my character simply built the exterior from salvaged parts.)
More details on the mod here: