66bit puzzle was a key between 2^65 and 2^66. The actual key was (in decimal notation) 46,346,217,550,346,335,726

The 67bit puzzle is a key between 2^66 and 2^67. So puzzle 67 has twice the number of keys to search as 66. Puzzle 67 has 6.7BTC currently. It might be "easier" than 66bit depending on how quickly GPUs advance in the coming years

Disclaimer, this whole thing could be a scam. But the rabbit hole goes deep!