What is Bottle hunting?

I was talking with a friend and she told me that her partner and son were out bottle hunting. 

When I first heard this, the image that came into my head was a plastic, 20 ounce Coca Cola bottle. I wondered what, besides cleaning up the environment, could possibly be the appeal in bottle hunting?

So I told my friend “I didn’t know bottle hunting was a thing.” She then proceeded to explain to me how they’ve excavated ancient bottles from as early as the 1700s! Now that makes a bit more sense, historical artifacts and things like that. I mean, bottles are still bottles, but there is a huge difference between a 20 ounce coke bottle from the bodega and a bottle from the 1800s that could contain significant financial and historical value.

So how many of you actually knew that bottle hunting was a thing?