I have been looking into this for days, but this plant is difficult to identify without its flower. I reached out to a botanist at Dartmouth, who suggests that it is either one of two species-- a nasturtium (Tropaeoleum sp.) or a geranium (pelargonium). The leaves are what are called peltate, meaning shield-like with the stem attached directly underneath.
!enter image description here
Source:
* Botanist at Dartmouth
* <
* * *
On further research, specifically of peltate leaves, this plant looks more like Umbilicus rupestris, which is commonly found in southern Europe and grows in damp rock crevices!
Source:
* <