No so hidden really. There are electrical outlets in the towers, and there is one in the backsplash set horizontally. It is behind the towels in this picture. Here is another shot.

Thanks for your helpful response ! Also are these plain mirrors or recessed mirrored medicine cabinets ?

Plain beveled mirrors set in a face frame. The medicine cabinets in this scheme are the towers on each side. I have done a version of this without towers and with medicine cabinets. I would say just to be careful to have a high enough splash so that the medicine cabinet doors clear the faucet fixtures.