Recently there was long thread about the BCA. I can now post possible answers to some of the questions, such as "Why is the BCA still raising membership prices when there is a significant amount still left in its coffers?"
Expect you could easily fit the Frozen Deep in the parts of Calder's Geo that don't get illuminated - it faces west & has a large headland to the south (between it & the sun!)
No, it's not the passage shown going through the headland, it's entrance is much smaller than the rest of it.
https://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-28965618