The Hamiltons owned huge areas of coalfield in southwest Scotland. A lot of the coal in that area is in shallow seams, and the ground is often wet. There was one appalling disaster when the miners struck upwards into a swamp. The mine owners' surveying and design could be pretty slapdash.

I think what's happened around the mausoleum is that the whole area around it has sunk. Last time I tried to visit it, there had been heavy rain, and the mausoleum was sitting inaccessibly in the middle of a lake which was normally parkland. Taking a few feet of coal out from under a flat plain tends to do that.

I'll look at your basilica pictures when I get to a faster computer. From what I can see, it seems to be intended as a replica of the basilica of Assisi, and coincidentally I got a book about that today. It has one musically interesting item: in the chapel of St Martin attached to it, there is a fresco by Simone Martini from 1316-ish depicting the life of St Martin, which has two musicians playing - one has a stringed instrument midway between a cobza and a mandolin, the other is playing a double pipe like the Sardinian launeddas or Greek aulos (the painter even got the rectangular fingerholes right). Unusual sound to hear in a church, if the painting implies that.