A series of caches placed along the Cochituate Aqueduct. They are intended to be easy (most of them) and winter friendly (most of them).
There are a total of SEVEN caches including the following:
Cochituate Aqueduct #1: GC6AK77
Cochituate Aqueduct #2: GC6AK7C
Cochituate Aqueduct #3: GC6AK7G
Cochituate Aqueduct #4: GC6AK7M
Cochituate Aqueduct #5: GC6AK7R
Cochituate Aqueduct #6: GC6AK7CZ
Cochituate Aqueduct Bonus: GC6AVVV
I recommend you read the information for the Bonus cache since finding that cache depends on information you get at each of the six regular caches.