A website that I have touted before is Bridge Hunter.  It is a user developed guide to the historic and interesting bridges in the United States.  Kind of a Wikipedia for bridges, it is very popular with engineers and others that like to see great engineering.

Recently I was asked by someone for advise on where to snorkel in Hawaii and by someone else for advise on where to snorkel in Belize.  I did a search for a Bridge Hunter equivalent for snorkeling and didn’t find one.  Since snorkeling is vastly more popular than looking at bridges it seems like it would easy and profitable to develop a user participation Snorkel Hunter web site.  It would also be a great service to the sport.

A few caveats.  Advertising would have to be low key and it would be important to keep travel consolidators like Expedia and Travelocity off the site.   Also make sure that the site is smart phone accessible and it has good maps.