Everyone needs a place to get away. It is unclear who built this location, but it definitely makes for a good hiding spot.
Immediately after entering, the party is faced with a door, in addition to whatever other obstacles the GM places in area 1. Area 2 provides hope that the sanctum is near with its large iron door. But area 3 will dash hopes as only a party that finds the secret passage will actually make it to the sanctum. That is, if they can get past the double iron doors leading to area 5. And area 4 provides a spot for an NPC encounter or even just a short rest.