Where it is, and what it actually is
Comino is a three-square-kilometre island between Malta and Gozo, almost uninhabited, with no village and no roads. The Blue Lagoon is the channel between Comino and the islet of Cominotto, shallow and sandy, which is what produces that translucent turquoise. There is no town and no infrastructure: a few kiosks in season, toilets, and that is it.
Getting there
Two main departure points. Cirkewwa, at Malta's northern tip, where crossings are shortest and cheapest, from around ten euros return. And Sliema, where the day cruises leave from, more comfortable but longer and dearer, often around thirty euros. From Gozo there are departures from Mgarr. Boats run continuously in summer, the first around 9am.
The hour that changes everything
This is the only advice that really counts. Between 11am and 4pm the lagoon is saturated and the beach effectively disappears. Take the first boat of the morning, around 9am, and you get two genuinely calm hours. Or come late afternoon as the day cruises head back. In May, June, September and early October the problem almost vanishes and the water is still warm.
What to bring
Water, plenty of it: the kiosks charge island prices and there is no supply. Sun cream, because there is almost no natural shade. Water shoes for the rocky sections. And cash, since not every kiosk takes cards. There is no locker or changing room: what you bring stays with you on the beach.
Comino's other coves
Almost everyone stops at the Blue Lagoon, which leaves the rest of the island empty. Santa Marija Bay, twenty minutes' walk away, has sand, trees for shade and twenty times fewer people. Crystal Lagoon, right next door, is deeper and reached by boat. Walking for fifteen minutes completely changes the day.
How it fits with a night out
Comino works as a morning and finishes in the early afternoon. That sits perfectly with a 5pm pool party or a 7pm boat party the same evening, as long as you take the 3pm or 4pm boat back. Plenty of groups do exactly that: Comino in the morning, a nap, then the night. It is the most efficient Maltese day there is.