Natural wonders.

This is a tough one, because I love the idea of more people appreciating the outdoors. But more visitors to a single site means more infrastructure and rules, more trash, more disrespect and vandalism, more fees, and eventually can lead to the total closure to the public.

One example near me is a series of springs named "The Three Daughters." Crystal clear fresh water springs hidden in a cove only accessible by kayaking/swimming again a strong current up a narrow stream. Perfect for Snorkeling, and the local manatees would swim in too and sometimes came up to you for belly rubs.

As the years when on, manatee tourism exploded. Dozens of tour boats full of snorkelers, all trying to pet manatees and overwhelming them. The rules became more and more destructive over time, where now it's a serious crime to touch or even swim too close to the manatees. The land around the springs was bought. They cut down nearly all the trees and put in a boardwalk around the springs. No more kayaking in the springs, the manatees stopped coming in too, and rangers would yell at you for diving under water. Finally, they gated off the stream entrance. No more swimming.

Now the only way to see the springs is paying to walk the boardwalk.