The Chapel is a stunning patch reef on Agincourt Reef No. 4 with a diverse array of corals and several swim-throughs, according to Silverseries and Poseidon. It is also described as perfect habitat for sea anemones and their resident clownfish, which makes it one of the best places on the Agincourt complex to find anemonefish. The reef is compact, with a maximum depth of around 18 m, and its coral cover is remarkably varied: plate corals stacked in tiers, rounded boulder corals, thickets of staghorn and sea fans growing from the sides.

The swim-throughs – short arches and tunnels formed by coral growth – give the site its name and a sense of entering and leaving small rooms as you pass through them. They are open and well lit, and suit divers with good buoyancy. Anemones carpet parts of the upper reef, each hosting clownfish, and it is common to see several species – including the orange-and-white Barrier Reef anemonefish and the darker spinecheek anemonefish.

Giant clams nestle in the coral, cuttlefish hover nearby, and turtles are regularly seen. Grey reef whaler sharks cruise around the patch reef's margins, and schools of baitfish swirl above, occasionally scattered by hunting trevally. The combination of swim-throughs, anemones and big-animal sightings makes The Chapel a well-rounded dive for all levels.

Most of the interest is in the top 12 m, so newer divers can enjoy it fully, and snorkellers get a good view of the anemones and clams. Visibility averages about 15 m and has been reported to 35 m. For photographers, clownfish in anemones provide endless macro subjects, while the swim-throughs offer wide-angle possibilities.

It is a gentle, rewarding site that shows off the coral diversity of the Agincourt ribbon reefs.

Agincourt day boats leave Crystalbrook Superyacht Marina (formerly the Reef Marina) on Wharf Street, Port Douglas, between about 8:00 and 8:30 am. Park in the marina car park or the free all-day street parking around Wharf and Dixie streets; Quicksilver, Poseidon and Calypso also run coach pick-ups from Port Douglas, Palm Cove and northern Cairns beaches. The run to the Agincourt ribbon reefs on the edge of the continental shelf is about 65–70 km north-east and takes roughly 75–90 minutes on the large catamarans (Silversonic is the fastest), longer on small-group boats such as Scuba IQ/Blue Dive.

You gear up on board and giant-stride from the dive deck at a permanent mooring; the skipper picks the sites on the day to suit wind and tide, so a named site is never guaranteed. Boats are back at the marina around 4:30 pm.

Agincourt is an outer ribbon reef on the shelf edge, so it is fully exposed to the south-east trade winds that blow from about April to September. Moorings on the protected western (back-reef) side remain diveable in 15–20 knots, but anything over 25 knots or a 2.5 m+ sea makes the crossing rough and operators may cancel or switch to more sheltered moorings. Calm spells in October–December give the glassiest days and 30 m+ visibility.

The wet season (December–April) brings northerlies, afternoon storms, cyclone risk and occasional reduced visibility after big rain events, although the outer reef is far less affected by run-off than inshore reefs. Marine stingers are present November–May. Tidal currents run along the reef edges and through the gaps between the Agincourt reefs; spring tides strengthen them, so exposed corners are usually dived on the neaps or near slack water.

Circle the patch reef at 12–15 m exploring the swim-throughs in single file with the guide, then come up to 6–8 m to explore the anemone fields and clam beds on the upper reef. Safety stop on the reef top near the mooring.

Quicksilver Silversonic – daily, 3 dives across Agincourt 1–4; Poseidon (Quicksilver Group) – daily, 3 sites at Agincourt; Calypso Reef Cruises – regular Agincourt days; Scuba IQ / Blue Dive and Tech Dive Academy – small-group day trips several days a week.