Wildlife swimming in Snæfellsnes

Each winter, huge shoals of herring pour into the fjords around Grundarfjörður on the Snæfellsnes peninsula, and the herring bring orcas — pods of killer whales that hunt them close to shore beneath the iconic Kirkjufell mountain.

On a specialist trip you can slip into the near-freezing water in a drysuit and snorkel in the vicinity of these wild orcas, hearing their calls and, on the best days, watching them pass beneath you in the dark blue.

It is one of the very few places on earth to attempt an in-water encounter with wild killer whales, and an intense, humbling one: cold, unpredictable and entirely on the whales' terms.

For experienced cold-water swimmers and wildlife obsessives, snorkelling with orcas under an Icelandic winter sky is about as wild and rare as ocean experiences get.

A specialist winter boat trip to find orcas hunting herring, with the chance to enter the water in a drysuit and snorkel near them when conditions and the whales allow.

This is serious cold-water activity: near-freezing sea, short winter daylight, and encounters that are never guaranteed and always on the animals' terms — you may see plenty from the boat and get little or no in-water time.

You must be a confident cold-water swimmer, comfortable in a drysuit with your face in dark, cold water, hence the high age limit. Operators supply the drysuit and brief you thoroughly, and keep a respectful, legal distance, letting the orcas choose the interaction.

Expect cold, waiting, and the possibility of an unforgettable few seconds with a wild killer whale — or of simply watching them from the deck.

Go in winter, roughly November to March, when the herring and orcas are in the fjords. Book a specialist in-water orca operator based around Grundarfjörður; these trips are limited, weather-dependent and not cheap.

You must be a strong, confident swimmer with cold-water comfort, and ideally some drysuit or snorkelling experience — be honest about your ability, as this is a demanding, cold environment. The operator provides the drysuit, hood, gloves and briefing; wear warm base layers.

Manage your expectations: sightings and especially in-water encounters depend entirely on the whales and the weather, and many trips are boat-based watching only. Follow the guide's rules on distance and behaviour to keep it safe and respectful for the animals.

When it works, it's one of the rarest wildlife experiences on the planet.