If and when the Gateway outpost is deployed in 2023, it will need an airlock to get any useful work done, so ESA is working on a new egress point for scientific experiments for the cislunar manned laboratory. Based on two independent approaches by Airbus and Thales Alenia Space, the final design will be part of the European module ESPRIT, which will also provide telecommunications and spacecraft refueling capabilities.
An airlock seems like a simple enough thing. It's a box with a pair of doors that can't both be opened at the same time while one is under pressure. It allows astronauts and equipment to enter and leave a spacecraft by equalizing pressure in the chamber without having to depressurize or pressurize the entire vehicle.
But designing one isn't that easy. Such airlocks tend to be cramped, full of equipment, and present all sorts of ergonomic problems – especially for weightless astronauts. To overcome this, ESA is currently testing a full-size mock-up of one of the airlocks built by Comex for Airbus in a swimming pool in Marseilles, France.