Access again - you might need something like a bendy bridge ramp or similar at the side of the corner house as well - so the hamster can get onto the house roof easily and get at the cork log to use it. He might be able to pull himself up on top of the house, but it's nice for them to have the option! Of an easy run up there or a pull up exercise if he's in the mood.
So basically a couple more bendy bridge ramps could be useful (or a rainbow bridge and a bendy bridge - rainbow bridges are always popular!). And perhaps another hidey place at floor area. In that corner where the sand dish is at the moment maybe with much deeper substrate it could be pushed down into. Coconut huts are popular or just home made ones made from a square tissue box or something.
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I have this coconut hut - the hole is definitely big enough for syrians on this one (you have to watch that).
Happy Pet Nature First Coconut Hut for Hamsters & Mice | Barks & Bu... - Barks & Bunnies
Bendy bridges can be a pain as some do have gaps that feet can get caught in so best you can see before you buy. One good place to put a bendy bridge for a ramp up to a house roof is - over the entrance door. This makes a tunnel entrance and makes the house dark inside and hamsters like that - plus it makes a good ramp onto the house roof.