Here are a bunch of GTA 5 Online Known Interiors & Enterable Locations by ts. These are great if you get a bounty on you, you can go inside and see how long you can last.
Airport building 1
The building on the left.
Airport building 2
Pacific Standard bank - One of the most detailed interiors available Online. Has multiple levels and paths.
Construction site - Has glass covering lots of sides of the building, multiple levels, and lots of cover. Makes an interesting place to dig in.
Fire Station Garage
Fire Station Tower
Los Santos Customs can be entered on foot by leaving your car near the garage door and walking in. There are a few different interiors for LSC.
The Mill out by Mt. Chiliad has somewhat of an interior and is an interesting place all around.
Impound garages behind this police station all open and close. The police station itself is locked in Online however, although it is open in SP.
The strip club can be entered with guns after shooting the guard outside and is a really detailed interior with a good amount of space. Did not include location because it is marked on map.
Sniper tower one of the only tall towers you can get on to and provides good cover. Must parachute onto it though. Haven't figured out a way to get down by myself yet.
Apartment complex tunnel The only entrance to this little area on foot is right through those doors on the outside, which lead to a pool area with good cover. The only other way in is through helicopter.
Los Santos Transit station You can ride the subway. There are more of these stations around the city.
House under construction 4 different levels to climb through. Small but semi interesting.
Rundown Motel Has a few rooms on the top floor that are usually occupied by the homeless.
Bar This is also where "darts" is on the map. Can be entered with guns.'
Airfield control tower
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