If you’re passing, say from Stromness to Kirkwall or Finstown, Unstan is near the road, and has parking.
If you aren’t sure about dark dingy tombs, it’s neither, the whitewashed modern ceiling and the skylights make it quite dry, and well illuminated. To the point where the stones are a vivid green on a bright day, due to the algae growing on them.
There are many inscriptions, you could lose an hour or so trying to decipher if any are prehistoric. Most seem to be 19thC