Bring a pen and paper for this one. It IS a puzzle cache.
Certain areas are only open from 10:00 - 5:00. The entire caching tour may take up to an hour. Plan accordingly.
Download the MP3. This is meant to be listened to "in the field". Listen it on a portable device (An MP3 player or burn it to a CD) A combination of a "soundseeing" tour and a puzzle cache.
Update 11/1/10 - The historical exhibit in the museum hallway is gone - replaced by little TV monitors - very sad! The 2nd digit of the surfboard is 0.
Update 1/4/16 - The Lilly pond plaque appears to have changed. It USED to be: 1986
PLEASE NOTE: The area described in the SECOND half of the audio has changed significantly. However, there is only one main path / walkway. If you follow it, trying to keep pace with the audio as best you can, you will end up near the right place and should recognize the final audio clues. Good luck!
Go here to get the MP3 audio file.