Pirate Rock is an off-the-grid swimming hole on the Upper Tioga River near Blossburg, in the rugged Tioga County country of north-central Pennsylvania. Its calling card is the water: startlingly clear, crystal-blue, and see-all-the-way-to-the-bottom transparent — a genuinely striking sight tucked back in the woods.

There's an important story behind that beautiful color, though. The remarkable clarity and blue tint come from acid mine drainage from old coal mining upstream, which has left this stretch of the Upper Tioga essentially sterile — clear as glass because little lives in it. It's a beautiful spot with a complicated past, so go in with eyes open about the water quality.

Reaching it takes some effort: from Blossburg, follow Main Street onto Gulick Street, bear right onto Ogdensburg Road for about 2.8 miles, and look for an unsigned dirt road on the left. From there it's a walk of under ten minutes along a path (with a small stream crossing) to a clearing by the water. There are no facilities of any kind.

Spring through early fall is the season — cooler water in April through June, warmer in July through September, and gorgeous foliage in autumn. Wear water shoes, watch depth and footing on the rocks, keep an eye on kids, and carry out all your trash.