For me, it would probably be the treasure trove of field stones we found, quite accidentally, when we built our house here.
We found this property in 2003 and one of my biggest disappointments was that there weren't any field stones to be found on the property. I always like to use them in gardens... Well, one day the contractor called us up and asked us to meet him at the property to stake out the corners of the new building. We took a tape measure and stakes and put them in place, then I took a look out across the property towards the west, told him to move it back further from the road a bit and tilt the building a little more to the north. So we lifted the stakes and tried again, I took another look and liked that spot better. The next day the excavators came out and started digging a 4 foot deep trench for the foundation. They started on the north wall and after a few feet started digging up nothing but field stones! They had hit the mortared, field stone foundation to an old building or farm house

After about 30 feet they reached the northeast corner, and as they turned to dig the east wall, that old foundation turned as well. At the exact same corner there were two huge corner stones, and then another 10 to 15 feet of field stones. By the end of the day we had a huge pile of field stones collected which Brian and I hauled away so we could use them later. The excavator asked if I knew that was there, and no, I had absolutely no idea. We knew there was a building somewhere in that general location at one time, but had no idea the foundation was there, let alone in the exact same spot as our new home.
We used all of those stones to line the pathway of our hosta garden out front - you can even see some of the mortar on a few of them. Here are a few in this picture of Hosta 'Nancy Gill', H. 'Crusader', and H. 'Golden Scepter' (click to enlarge).
Thanks for asking!
Chris