Overnight stays in a lighthouse or its keeper's house, run by the nonprofit, foundation, concession or owner that keeps the light, and booked on that operator's own site.
The standard is the operator's own statement that you sleep at the light station and book with them directly. The United States Lighthouse Society keeps the national list of lighthouse lodging; this club uses it as a source, not as a rule.

Most lighthouses you can sleep in are kept by a small nonprofit, a friends group, a historical society or a family, and the room fees pay for paint, roofs and lenses. Their booking pages are scattered and easy to miss behind Airbnb and recreation.gov listings. This club collects the ones you can book straight from the keeper.
Twelve stays from twelve operators in nine states, from Newport to Puget Sound. Each links to the operator; you book with them.
Preview from East Brother Light Station, Inc.'s listing
Preview from WR Trillium Inc's listing
Preview from Lake County Historical Society's listingVerified stays held back for count, lighthouses that book only through a marketplace or a rental agency, closed programs, and the authority lists.