The two have been bridged together with a removable section made from hardboard and a couple cleats to secure it in place. Additional ramps, beds, soft-cubes, and an old footstool finish it off.
Hobbes, as an unusually large cat, has gravitated to the bridge in the centre which allows him space to sprawl. That in itself has made the project worthwhile.
Admittedly, this might be just a little excessive...
Grin!