This environment is part of the Atari environments. Please read that page first for general information.

Action Space


Observation Space

(210, 160, 3)

Observation High


Observation Low





Your job is to defend the submerged city of Atlantis. Your enemies slowly descend towards the city and you must destroy them before they reach striking distance. To this end, you control three defense posts. You lose if your enemies manage to destroy all seven of Atlantis’ installations. You may rebuild installations after you have fought of a wave of enemies and scored a sufficient number of points. Detailed documentation can be found on the AtariAge page.


By default, all actions that can be performed on an Atari 2600 are available in this environment. However, if you use v0 or v4 or specify full_action_space=False during initialization, only a reduced number of actions (those that are meaningful in this game) are available. The reduced action space may depend on the flavor of the environment (the combination of mode and difficulty). The reduced action space for the default flavor looks like this:












By default, the environment returns the RGB image that is displayed to human players as an observation. However, it is possible to observe

  • The 128 Bytes of RAM of the console

  • A grayscale image

instead. The respective observation spaces are

  • Box([0 ... 0], [255 ... 255], (128,), uint8)

  • Box([[0 ... 0] ... [0  ... 0]], [[255 ... 255] ... [255  ... 255]], (250, 160), uint8)

respectively. The general article on Atari environments outlines different ways to instantiate corresponding environments via gym.make.


You score points for destroying enemies, keeping installations protected during attack waves. You score more points if you manage to destroy your enemies with one of the outer defense posts. For a more detailed documentation, see the AtariAge page.


env = gym.make("ALE/Atlantis-v5")

The various ways to configure the environment are described in detail in the article on Atari environments. It is possible to specify various flavors of the environment via the keyword arguments difficulty and mode. A flavor is a combination of a game mode and a difficulty setting.


Valid Modes

Valid Difficulties

Default Mode


[0, ..., 3]



You may use the suffix “-ram” to switch to the RAM observation space. In v0 and v4, the suffixes “Deterministic” and “NoFrameskip” are available. These are no longer supported in v5. In order to obtain equivalent behavior, pass keyword arguments to gym.make as outlined in the general article on Atari environments. The versions v0 and v4 are not contained in the “ALE” namespace. I.e. they are instantiated via gym.make("Amidar-v0").

Version History#

A thorough discussion of the intricate differences between the versions and configurations can be found in the general article on Atari environments.

  • v5: Stickiness was added back and stochastic frameskipping was removed. The entire action space is used by default. The environments are now in the “ALE” namespace.

  • v4: Stickiness of actions was removed

  • v0: Initial versions release (1.0.0)