Some traps aren't really traps at all, but are part of the landscape that end up with trap-like effects. For example:
Goblin Privy (CR 2)
A small wooden door is set into the wall.
Type: mechanical; Perception DC 18; Disable Device 19
Trigger location; Reset None
When a PC opens the door, the sight and smell of the room beyond is... sickening. Goblin Privy (DC 18 Fortitude Save or become nauseated for 1d6 rounds); multiple targets(all targets within 30 feet)
Think about all the rooms and equipment that might be in your dungeon, whether it be an ancient Dwarven underground fortress, an illithid lair or goblin stronghold. Hazards, both lethal and non-lethal, are likely to be behind lots of doors. Rather than either having lots of empty rooms or just a few rooms, add some character into your dungeon that doesn't just have flavor text, but also has concrete effects. Remember, even goblins gotta pee somewhere, too.