Drill a big hole through the back of the cupboard and take an ethernet cable out of it.
Seriously it's a lot easier than it sounds.
What is on the other side of the wall of the cupboard? If it is the outside then figure out where you can run cable (in conduit) to that gets close to the bar / garden room. Then install an AP ( possibly an outdoors one) there.
Drill a big hole through the back of the cupboard and take an ethernet cable out of it.
Seriously it's a lot easier than it sounds.
What is on the other side of the wall of the cupboard? If it is the outside then figure out where you can run cable (in conduit) to that gets close to the bar / garden room. Then install an AP ( possibly an outdoors one) there.