Don't think this classifies as an iwagumi but here! 6 gallon cube using a "pathway" to the cave. This was scaped to fit the needs of wild bettas who like to have hiding spots. Pretty recent scape so no chance to have it filled in yet.
I also plan on doing a lava rock scape loosely based on some coastal stacks I photographed in Iceland. If you look up Galapagos Stone Iwagumi there is a nice example of one Aquarium Gardens created and it's on YouTube. Also, I think around page 7-9 of the journals there is one that is more of a diorama than classic Iwagumi.