Challenge Cache: A type of cache where you not only have to sign the log, but also complete a challenge. This cache is located at the posted coordinates.
This Challenge: You must have found a cache in a total of 500 grid squares. You can count up to 81 squares for EACH Canadian Province or US State. Each DT grid square to contribute to this total must have at least one cache found.
Specifications: For example,
- if you've found at least one cache in all 81 DT grid squares for caches in Ohio, that counts as 81 squares toward your total
- if you've found at least one cache in 30 grid squares for caches in Ontario, that counts as 30 more squares toward your total
- if you've found no caches in Texas, that means you have to cache more in Texas. And your total is not increased at all.
- if you've got 2 DT fizzy grids in Ohio (2 caches in each of the 81 grid squares), this counts as 81 squares toward your total (not 81x2)
Check your qualifications here:
My qualifications: 
I have filled 960 DT cells among all DT grids. (required: 500)