Saipan & Tinian · Northern Mariana Islands · Cave & cavern · Wall
The Grotto
Three underwater holes lead out of the cavern into open ocean
A limestone cavern on Saipan's north-east coast, connected to the open Pacific by three wide openings at depths between the surface and 18 m. Divers giant-stride into the pool inside the cave, swim out through one of the holes, and explore the walls, caves and swim-throughs on the outside. Visibility is the best Saipan has to offer, typically over 30 m.
Where it is and how deep
15.2605° N, 145.8240° EApproximate position — the dashed circle shows where the site lies; your operator's briefing has the mooring.
The dive
You giant-stride from the rock inside the cavern into about 5 m of water and hold onto the mooring buoy until every member of the group is in. From there the cave floor falls away into the tunnel, and three wide openings lead out to the open ocean at depths anywhere between the surface and 18 m. The deepest sections of the cavern itself go to around 20 m.
Once outside, it turns into a wall dive: walls, swim-throughs and caves along the cliff face, and a chamber divers call the batcave, where bubble coral and lace coral grow. One to three white-tip reef sharks are usually somewhere in or around the Grotto, along with a small group of barracuda and pyramid butterflyfish.
Green sea turtles, Napoleon wrasse, tuna and spotted eagle rays all turn up here, though none of them reliably. The dive is planned to finish the way it started, back in through one of the openings and up in the cavern pool, rather than surfacing outside on the ocean side of the cliff.
Marine life and season
- Reef sharks
- Barracuda
- Sea turtles
- Napoleon wrasse
- Tuna
- Eagle rays
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Prime | Prime | Prime | Prime | Prime | Good | Fair | Fair | Fair | Fair | Good | Prime |
Season follows Saipan & Tinian: Dec–Jun is calmest and clearest; Jul–Nov is typhoon season, when swell regularly closes the Grotto entirely.
Know before you go
- Never plan to surface outside the cavern: getting out is sometimes easy, but getting back in can be impossible against strong current, whitewater breaking on the cliff and sharp rock.
- The 112-step staircase has to be climbed again with a tank on your back, so divers taking this site from shore should be in good physical condition.
Dive videos
The Grotto - Saipan - CNMI · Oleg Shishko on YouTube
Questions divers ask
How deep is the Grotto?+
The three openings that lead out to the ocean sit at depths between the surface and 18 m, and the deepest sections of the cavern reach about 20 m. Divers enter in around 5 m of water beside the mooring buoy.
Can beginners dive the Grotto?+
It is normally kept for divers who are already certified, and it is one of the most challenging dives on Saipan. Only on rare rough-weather days, when every other site is undivable, are open water students and introductory divers brought here.
Sources
- Diving in Saipan — Wikivoyage
- Saipan — Wikipedia
Photo credits
- One of the Grotto's underwater rock openings glowing turquoise as light filters in from the ocean beyond by Derek Hatfield from Peterborough, Canada, CC BY 2.0, via Wikimedia Commons
In The Logbook
- How far you can see underwaterOcean science · 12 min read
- How much weight do you need to dive?Gear & kit · 8 min read
- Cavern and cenote diving without cave trainingCaves & caverns · 8 min read
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