"Develop your mercenaries' different stats. Train them, so they become the ultimate killing machines!"
In this building you can level the mercenaries you have unlocked up to level 6. You can have 2 of these buildings which means you can have 2 active training going on at the same time. Higher level Training Chambers are required to train higher level mercenaries
Extra Training Chambers
To build the 2nd Training Chambers you need City Center level 5 and Recruitment Chamber Level 2.