You signed the contract.
Do one of the options written in the contract.
option 1 - Hand in resignation letter to BRK and work the 3 months notice.
option 2 - Hand in the resignation letter along with 5000 euro and leave ASAP
Do not just leave and pay nothing.I have 'heard' they chase you and in the unlucky event of traveling on a Ryanair flight in the future - you will be flagged up.
They may also be nasty enough to somehow contact the place you are going or give you a bad reference if you need one.
I know you don't have to tell them where you are going,but you never know - your next employer might ring Ryanair up to 'enquire' about you out of the blue.Then your bunched
Its very difficult - but just play the game and give them a crocodile smile as you leave.Most of us will be in this position some day if things don't improve significantly in the interim.