You can go through the code here:

  
      github.com
  
  
    openai/gym/blob/master/gym/core.py 134
from gym import logger

import gym
from gym import error
from gym.utils import closer

env_closer = closer.Closer()

# Env-related abstractions

class Env(object):
    """The main OpenAI Gym class. It encapsulates an environment with
    arbitrary behind-the-scenes dynamics. An environment can be
    partially or fully observed.

    The main API methods that users of this class need to know are:

        step
        reset
        render


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As far as I know,  there is a core super class called gym.Env and there are other sub classes of this to implement different environments (CartPoleEnv, MountainCarEnv etc). This unwrapped property is used to get the underlying gym.Env object from other environments.