Because my players' suspension of disbelief began to suffer when exploring more "normal" dungeons, I have created some big dungeons which are based on bigger,
realistic structures: castles, towns, military structures, bunkers, etc.
However, another problem has come up. A structure which is able to hold a regiment contains many repetitions: kitchen, bathroom, sleeping room, again and again, because a place where people live is more utilitarian than most fantasy dungeon designs.
Now my group isn't suffering a lack of suspension of disbelief, but I suspect they are a bit overwhelmed: their normal routine of sifting through every room is not possible anymore, and they get restless. I suspect they fear losing out on interesting information now that the dungeon isn't linear.
I am not sure how to keep the players busy and focused in a dungeon that has many equal rooms. How can I GM these larger structures without the players becoming frustrated in this way?
Some information about the current background. The group explores the structure with a map which is under a glass plate covered by rice (sand is leaking too much for my taste). The advantage is that I do not need to describe every room and they can make maps (naturally I have the master map with undiscovered features like traps, hidden rooms etc.), the disadvantage is that they realize how vast the structure is and that I gave them the freedom to explore.
The structure itself has a very specific and very important purpose which is the reason why it is so vast, the constructors had no choice. The reason was temporary, so the inhabitants left bit by bit. The inhabitants and their reason to live there changed rooms and build hidden ones without never finding all rooms of their predecessors. So the current explorers (my group) find plundered and vandalized old rooms and sometimes an older trap which is not working anymore. But the last sessions they found out that someone left fresh traps and a message that their presence is not welcome >:)