Here are the locations of all Bonus Levels.
No tombstone unturned
(Access all bonus levels in Zombies.)
1) Level 1 – by a house (top centre).
You must pick up either a bazooka or monster potion to break the hedge.
2) Level 9 – by toxic containers (top centre )
Again, use either a monster vial or shoot through.
3) Level 12 – save all cheerleaders and you’ll be taken to the bonus level automatically.
Currently, this bonus level doesn’t count towards accessed maps.
4) Level 17 – behind cob-webs next to the room with a monster vial (top centre)
5) Level 22 – via hidden passage in a laboratory.
There’s also a hidden, powerful flamer next to the bonus level pick-up!
6) Level 33 – in top left corner, in water area.