The Portland Head Light

The oldest lighthouse on the coast of Maine is located at Cape Elizabeth, just south of Portland. It was commissioned by president-elect George Washington in 1787, finished four years later, and you can read more about it here:
Portland Head Light

From the perspective of aesthetics the coast of Maine is beautiful, but from the perspective of navigation it's a nightmare out of the fiction of Lovecraft. Much of the coast was encased in kilometers of ice until just a few millennia ago, and when the glaciers retreated they carved deep jagged gashes into the bedrock from New Hampshire to New Brunswick. As the oceans warmed and expanded, the valleys turned to fjords and the hills into a vast field of islands and reefs. There simply hasn't been time for erosion to temper the sharp will of the land, so the lighthouses of Maine are an essential part of keeping ship traffic bound for Portland, Bath, and Bar Harbor afloat.

Lighthouses are charming in part because they're so practical. The need to not run your ship aground on a sharp piece of granite dictates function essentially the same way whether you pilot a clipper, a trawler, or the Queen Mary 2. There's thus little need to ever update a lighthouse's exterior, so even as the whale oil lamps are replaced with arc lamps, the house itself timelessly blinks on.