Both are sold from the same kiosks, at similar prices, described in similar language. They are not similar activities, and the assumptions people make about which is harder are frequently backwards.
What coasteering actually involves
Moving along a rocky shoreline by a combination of climbing, scrambling, swimming and jumping into the sea from height.
Sold as suitable for anybody reasonably fit. It is more demanding than that suggests.
The swimming is in moving water, in a wetsuit, wearing a helmet and buoyancy aid, frequently in swell. It is nothing like swimming in a pool, and people who describe themselves as confident swimmers sometimes find it difficult.
The scrambling is on wet rock covered in barnacles and algae, which is both slippery and abrasive. Cuts and scrapes are normal rather than exceptional.
And the jumping is optional in every operation I have encountered, which is worth knowing because people talk themselves into jumps they do not want to make.
The physical demand is real. Two hours of it is genuinely tiring, and cold is a factor even in a wetsuit.
What makes it good
Having listed the demands, it is among the more memorable things I have done on a coast.
You get to places that are unreachable any other way — caves, gullies, small coves accessible only from the water.
The perspective is different. Being in the water at the base of a cliff is a completely different relationship with a coastline than looking at it from above.
And the good operators are genuinely knowledgeable about the specific stretch they work, which turns it into a guided introduction to the geology and the wildlife as much as an activity.
Sea kayaking is more accessible than it looks
The reverse case. It appears to require skill and fitness and mostly does not, at the level it is offered to visitors.
A stable sit-on-top kayak in sheltered water is manageable by almost anybody within about fifteen minutes. The basic stroke is intuitive and the boats are extremely difficult to capsize.
The physical demand is moderate and paced by the group. Guided trips move slowly and stop frequently.
And the skill required for the guided version is close to none, because the guide is making all the decisions that matter.
Where sea kayaking becomes serious
The distinction that matters and is frequently blurred in marketing.
Guided trips in sheltered water are recreational. Independent sea kayaking on an open coast is a genuine discipline requiring navigation, weather assessment, rescue skills and equipment.
The gap between those two is enormous, and the equipment is different — a sit-on-top in a bay is a different craft from a sea kayak crossing open water.
People who enjoy the guided version and then hire a boat independently are the ones who get into difficulty, because the hire company is not making the decisions the guide was.
Wind is the specific problem. A kayak is a sail. An offshore wind that is barely noticeable on land will push a kayak away from shore faster than most people can paddle back.
What to ask before booking either
Group size and guide ratio, which for coasteering should be small and which is the main determinant of both safety and enjoyment.
What happens if conditions are poor. Both activities are condition-dependent and operators who never cancel are operating in conditions they should not.
Wetsuit thickness and whether boots and gloves are provided, which for coasteering in cooler water is the difference between two enjoyable hours and two cold ones.
What the swim distances are, for coasteering, which varies enormously between operators on the same stretch of coast.
And whether jumping is compulsory, which it should never be and which is worth confirming.
Who should do which
Coasteering suits people who are confident in water, reasonably fit, comfortable being cold and wet, and not troubled by heights. It does not suit anyone unsure about any of those, and there is no partial version.
Sea kayaking suits nearly everybody in its guided form, including people with limited fitness, and it is the better option for mixed groups and for anybody wanting to see a coastline rather than to be challenged by it.
The mistake I see most is groups booking coasteering because it sounds more adventurous, and then containing one person who is having a genuinely difficult time and cannot leave halfway through.
What it costs and what varies
Prices for both are broadly similar on most coasts, which is misleading because what you get varies enormously.
Duration is the main variable. A two hour coasteering session and a four hour one are advertised similarly and are different experiences, and the longer one is where the interesting sections tend to be.
Equipment quality is the other. A worn wetsuit in cold water ruins a session, and it is worth asking about thickness and condition rather than assuming.
Photographs are frequently offered afterwards at a price. Whether that is worth it is personal, and it is worth knowing in advance rather than being presented with it wet and tired at the end.