The limestone towers rising from Ao Nang's bay are older than the Himalayas — Permian reef carbonate, laid down roughly 250 million years ago when this coast lay beneath a shallow tropical sea. Wind and rain since then have hollowed them into the karst pinnacles that give Krabi its silhouette. Boats have threaded between them for centuries. The 7 islands sunset tour krabi operators run today follows a route that fishing families from Ao Nam Mao and Ao Nang worked long before tourism arrived. The waters fall inside Hat Noppharat Thara–Mu Ko Phi Phi National Park, gazetted in 1983 and administered from Ao Nang, Mueang Krabi District, Krabi 81180. Protection came late but decisively. The park now covers reef flats, mangrove fringes and the sand causeway of Thale Waek, the tidal spit that joins Koh Tup, Koh Mor and Koh Kai for a few hours either side of low water. A national park conservation fee of 400 THB per foreign adult funds ranger patrols, mooring buoys and reef monitoring. Park waters are open 08:00–16:30 daily. Seven is a working count rather than a fixed geography. Chicken Island, Tup, Mor, Poda, Si, Hong and the outlying stacks appear in most itineraries, with the sequence set by tide and swell on the day. Krabi evening island-hopping boat tours differ from morning departures in more than light: reef edges that hold snorkelling crowds at eleven are empty at four, and the water off Poda flattens as the afternoon breeze drops. Speedboat operators running the Phi Phi crossing add Maya Bay and Pileh Lagoon to the roster before turning back east. What distinguishes an evening departure is what happens after the sun goes. Bioluminescent plankton — dinoflagellates that flash when disturbed — concentrate in the sheltered bays through the warm months, and a swim after dark turns each stroke into a scatter of blue-green light. The phenomenon is unreliable, brightest on moonless nights and in calm water, and no operator can promise it. Beach barbecues on Phi Phi and buffet dinners served on the sand at Poda have become the fixed second act of the day. The longtail itself deserves note. Its hua thong prow ribbons are offerings to Mae Ya Nang, the spirit of the boat; its engine is a truck motor on a long driveshaft, an improvisation from the 1960s that remains the most practical craft for beaching on unmade sand. Speedboats reach Phi Phi in under an hour, longtails take the closer Krabi 4 Islands circuit at a slower, quieter pace, and both are offered as 7 islands sunset tour krabi tours from the same Ao Nang shoreline. The choice between them shapes the whole evening — reach, or intimacy.