I'm amazed by those holes at the centres of your slabs. Have the same here. Must be an artifact of the thermodynamic properties of a slab of concrete. I'm geekly fascinated
Ah Coleridge's place, know it quite well as we go to a campsite just out of Watchet (Blue Anchor side) a few times a year. You are right in the sweet spot I would think.
You need a million candle torch run by a car battery like for my Celestron. Or just one of these new-fangled Lumens lights like Mapanz has been talking about.