Laguna Grande Bioluminescent Bay

One of the most popular sights in the east is Laguna Grande, a bioluminescent lagoon in the Cabezas de San Juan Nature Reserve that glows on moonless nights. One of three in Puerto Rico (the others are Bahía Mosquito on Vieques and La Parguera Bay in the south), Laguna Grande is especially popular because of its close proximity to San Juan.

It's a magical experience: by kayak you start off in a virtual cave of mangroves until you slowly break out into open sky where you are dazzled by millions of stars overhead. As your eyes adjust, look down! Below, a surreal blue glow follows the movement of your paddle as it moves through the water, fish outlined in blue as they dart past. The unreal and eerie glow is created by trillions of microscopic dinoflagellates reacting to movement in the water.

Options for seeing the glowing waters include:

Kayaking Guided kayak trips are the most popular way to experience the lagoon. They have the least impact on the dinoflagellates and get you closest to the glow. However, with several different agencies providing tours, it can get crowded. Add to that paddling through mangroves at night and mishaps can happen, slowing down the group.

Electric boat Glide across the waters with ecofriendly Bio Island, which runs tours that last a little over an hour on a six-passenger boat. Guides explain the why behind the glow.

Walking tour Experience the glow on a nighttime walking tour offered at Cabezas de San Juan Reserva Natural. You tour the grounds by foot and tram and then spend time at the lagoon walking along boardwalks. Tours end at the lighthouse where you contrast the bay's dim glow to the encroaching luminosity of civilization.

Tour reservations Be sure to book any tour of Laguna Grande as far in advance as possible as trips fill up quickly. Note: A full moon makes the water's glow hard to discern. The rainy season, from August to November, can result in murky runoff that also diminishes the experience. Finally, be sure to avoid rogue operators that use nonelectric boats, which can contaminate the water and kill the dinoflagellates.

Swimming is prohibited at all times, whichever way you visit.