1000 Brussels, Belgium
This one is not for the faint of heart or body. This trail is described as a hiking trail but it is closer to mountaineering than it is to hiking. There are 2 places were you must use a rope (read:climb) to get up and down. It is nearly straight up and can be very muddy and slick. I did not make it to the lagoon due my being in sandals (remember described as a "hike") but none the less, it was a great experience. You will be muddy, likely tired (depending on your fitness level) and at least somewhat sketched out by the end, but I highly advise trying it. You can wash off in the ocean, just a few hundred feet away in what is likely the most beautiful cove in the world.
Railay Beach Lagoon Hike