Operation Abyss (zm_abyss) is an official Zombie mode map in Counter-Strike Online.
Abyss is the first zombie mode map released in the game. It takes place in the underground laboratory of the Rex Institute after the bombing incident. The map is quite dark and there are many obstacles inside it.
It is recommended to teamwork with your comrades since this map has bad defense for humans.
Although the Terrorists had successfully destroyed the chemical and biological weapons laboratory research facility known as the Rex Research Institute through bombing, the explosion woke up the biochemical monsters which were locked up deep in the depths of the basement...