Lot's Wife, Japan
|Pacific Ocean||Torishima||Pacific Ocean|
|Pacific Ocean||Lot's Wife||Pacific Ocean|
|Pacific Ocean||Pacific Ocean||Pacific Ocean|
Lot's Wife (Sōfu Iwa or 孀婦岩) is the southernmost island in the Izu archipelago. According to the English Wikipedia, it is 84m long by 56m wide. Its footprint is therefore at most 4704 square meters. Since it is the only land in the graticule, the odds against a land geohash on any given day are over 2,000,000 to 1.
This graticule is surely in the running for the smallest (nonzero) land fraction of any graticule in the world.
(Note: Since the grat map to the right won't help you find it, here's a better one.)