Gas giants are large worlds that have extremely dense atmospheres and very strong gravity. The atmosphere is so dense that it is liquefied and forms a incredibly deep ocean world. It is possible to dive into the ocean of liquefied gasses with a submarine or a submersible spacecraft.
Gas giants are normally rich in various atmospheric resources which can be harvested using harvester bay equipped spacecraft. This is normally also very advantageous as the high atmosphere density means greater harvest yields.
Harvester bay: Atmospheric Condenser Bay
Harvester bay: Particle Collector Bay
Construction on a gas giant is an extra harsh environment, it requires the building blueprints to have life support gravity modules to counteract the strong gravity. This can be circumvented by using a biodome, since it protects all buildings inside it.