Down in the South Pacific lies a little archipelago called the Yap Islands. They are inhabited by a Polynesian tribe, the Yapese, and are notable for their money. They have a rock solid currency. In fact, they use stone discs up to 12 feet across as "coins". (This is a bit historical - these days they also use the more convenient US dollar.)
For centuries the Yapese have prized stone discs because of the difficulty in obtaining them. They have to travel hundreds of miles in canoes, carve the discs out of calcite deposits and transport them back to the Yap Islands, also by canoe.
When a Yapese "spends" his stone disc the disc itself doesn't necessarily have to move. They leave them littered over the islands and everyone knows who owns which disc. In fact sometimes the discs fall into the sea during transport and are lost forever from view, but they can still be spent - everyone knows it's there under the waves which is good enough.
In the North Atlantic there's another group of islands where the natives do much the same, only with houses. That's us.