Mobs Spawns in impossible spots

I have a big box of villagers where you have to parkour to get into and a big base either lights surrounding everywhere but mobs seem to spawn everywhere, even more than before and I added even more lights. In my villager box, a creeper spawned even though there's no possible way in can parkour in or spawn in, there's a torch on every block on the wall. My difficulty is on normal but the mobs are so plentiful.