"A blue hole is a cave (inland) or underwater sinkhole. They are also called vertical caves .....Blue holes are roughly circular, steep-walled depressions, and so named for the dramatic contrast between the dark blue, deep waters of their depths and the lighter blue of the shallows around them." (Wiki - see http://en.wikipedia.org/wiki/Blue_hole )
Do you know of another WHS we could connect to Blue Holes?
A connection should:
- Not be "self evident"
- Link at least 3 different sites
- Not duplicate or merely subdivide the "Category" assignment already identified on this site.
- Add some knowledge or insight (whether significant or trivial!) about WHS for the users of this site
- Be explained, with reference to a source