New cacti for my collection

We were in a private garden in Sicily on part of a Mediterranean Plants and Gardens tour www.medpag.org and we walked through an archway to be greeted by, what seemed to be hundreds of, very large E. grusoniis, all happily growing away. A sight to see! We've also seen the ones in the Sydney Botanics but these Sicilian ones were on another level. We've (did have) a very large one in the garden under cover, sourced from Cornwall, but unfortunately one day I decided it looked a little bit dry, so I watered it with a hose. Big mistake! One exact hemisphere completely rotted and dissolved in about 24 hours or so. You'd think I had watered it with high strength acid! The other half is still there but has curled in on itself so is now much smaller. Moral: don't water cactus.