Im working on a city builder[0] where you can see inside homes. Expanding on point 1...
1. The streets have their own graph, as does each individual building. There's an address book; each building stores the driveway tile connecting to the street graph here.
2. Pathing inside homes uses A*. In order to make this extra fast, I bake the 8-directional egress weights for each tile in the building/yard.
2b. This gets condensed down into a 16-bit bitmask (2 bit chunks, 8 directions) and then stored in a hash table
2c. Each bit-chunk has four possible states:
FULL_BLOCK (e.g. a wall)
HARD_BLOCK (e.g. a large object that prevents walking through the tile from any direction)
SOFT_BLOCK (e.g. a smaller object that prevents passage on one edge)
NO_BLOCK (e.g. an unoccupied tile, or a tile with a tiny object)
This way a unit pathing inside a building does not need to check for obstacles on every tile. This also allows units to pass through tiles with objects provided the object is not huge and is rotated in such a way that the exit and entrance edge is not blocked. Lastly, an agent can still walk through a wall if the player e.g. forgot to place a door, to prevent the simulation from breaking down.
3. I use a waypoint system (stored in a queue) for agents so they can traverse through the different graph hierarchies with ease. This is also used to e.g. tell the unit to walk to their car first if they are driving.
4. Pathing on the street uses a different method (though still utilizes a baked graph) that makes it extra zippy.
[0] https://store.steampowered.com/app/2287430/Metropolis_1998/