puzzle140.com
Somebody hid it in 2017 and left a clue on the blockchain. Nobody has found it yet. Open a tab, lend your machine to the swarm, and watch how far we get.
the swarm right now
No download, no account, no deposit. It runs in this tab and stops when you close it.
Waypoints you have already sent stay with the pool even after you leave.
A match is made of two waypoints from two different machines, so no single browser can spot it — the server recovers the key and builds the transaction. That is true of every kangaroo pool, and it is why all of this is open: read the code, including the part that spends the coins.