Saw this activity HERE a few days ago and knew my boys and I would have to give this one a try. And sure enough, it was a big hit!
Simply freeze odd toys and trinkets in a dish of water (I followed a hint from the original site and did ours in layers so toys were all through the ice).
When the block is frozen solid, dump it out and arm your kiddos with toothbrushes, spray bottles, droppers for hot water, and anything else that may aid in treasure excavation. Then let them go at it!
Both boys were still going strong when the heat and naptime caught us and we all went in. We put the remaining ice block back in the freezer for later.
I can't imagine how long they would have lasted... but I wouldn't be surprised to see them go from start to finish sometime. Because we'll definitely be doing this again!