The remote north of Islay is littered with natural arches, in particular the area around Bholsa. Here is an attempt of a view through two of them at once.
I’m not sure how many of this type there are on Islay, this is a natural arch going over the sea and it is possible to (carefully) walk over it. Most of the other natural arches (I know of) are over dry land. This one is on the west coast of the Rhinns of Islay, not far from Lossit Bay (just visible in the background).