Oh I do like James Turrell, I went to see his 'deer shelter' at the yorkshire sculpture park. That's a similar thing, you sit in an old building (the deer shelter), and everything's pale and tomblike and still and contemplative. And up above you is a hole so you can only see the sky, so you can lie there (on the uncomfortable benches) and gaze at the movement of the clouds, watch the light change and so on. I thought it was great and luckily I had it to myself.

Your sky crater looks like a step onward, it looks less tomb like but with the grass all round you more natural, you maybe feel more like you're 'in' the environment rather than observing it? It looks very much worth a visit. Preferably on a warmish day and when there aren't hundreds of people.

I think there are definite links with tma=ish themes as you say. What with the banks sealing you off from external reality - like banks and ditches at henges. And you even get a visually similar effect at hill forts today, without the bustle of people in their round houses of course, it's just you and a flat expanse with high banks limiting your view of the surrounding landscape.

And of course in your sky crater there's the tomb-like stone passage you use to enter the crater. And in the centre, a very altar-like / coffiny slab that you can lie on. which is bound to conjure more thoughts of a Life and Death nature.