Blue Box Sanctuary

You conjure a blue box (10 ft tall × 5 ft wide × 5 ft deep) that opens into an interdimensional 2-bedroom cottage of roughly 900 sq. ft. The cottage includes; a living space, kitchen, washroom.
Access Control: Only up to 8 invited creatures may enter. Uninvited creatures must succeed on a Wisdom saving throw (DC = your spell save DC) to attempt entry; failure sees only an empty space. If someone knocks on the door, the caster can verbally grant entry, magically unlocking the invitation for that creature only. Inside, any creature inside can look through and a 5 ft. square directly in front of the door’s exterior as if looking through a window. 
Interior: The space inside is fully furnished and designed at the caster's discretion. Furnishings will be comfortable. When you cast the spell again, the interior looks the same as last time (unless you choose to redesign it). 
Sound & Light: Interior is isolated; sound, light, and smells do not pass outside. Any knocks or deliberate attempts to make noise on the exterior of the door can be heard clearly inside (as if through a thin wall). Normal outside noise (like a battlefield, animals, ect) does not bleed through—only direct interaction with the door.
Destruction: If the Blue Box is destroyed while creatures are inside, they and all items are expelled to the location the exterior occupied.
Storage: Items left inside remain in the cottage even after the spell ends. Items inside are safe from nonmagical tampering, but spells that specifically interact with extradimensional spaces (Dispel Magic, Teleportation, etc.) can affect them at DM discretion

Upcasting:
Bigger Interior: Each slot above 4th expands interior by 50% (5th = 1,350 sq. ft., 6th = 1,800 sq. ft., etc.).
Longer Duration: Each slot above 4th increases duration by 4 hours (max 24 hours).
Each upcasts allows 1 additional creature.
Level 6 or higher: Furnishings can be opulent or extravagant.