EVA Preparation Room
Every crew exiting the Hab for an Extra Vehicular Activity (EVA) must spend time to simulate decompression in the airlock. This is because the average pressure on Mars equals that we can find at 35 km above Earth: 0.6% from the pressure we know here on Earth. The effects of low pressure on the human body are starting only now to be studied and understood. See Human adaptation to spaceflight (Wikipedia) for more info.
Used for access to areas that don't require a space-suit – e.g. the Greenhouse and Observatory (which for the purposes of simulation, are accessed via pretend 'pressurised tunnels'); or for 'outside of simulation' activities – e.g. checking the generator, etc.