Sea Life London Aquarium

The air changes as you go down. It turns cooler and a little damp, with a faint smell of salt and wet stone. The daylight of the South Bank fades behind you, and a soft blue glow takes its place. Somewhere close by, pumps hum steadily. Up above, the London Eye turns and crowds stream across Westminster Bridge. Down here, the city goes quiet. Water fills the walls around you, and the only movement is slow, silver, and alive.

First, a word about where you are standing. This aquarium sits inside County Hall, the grand stone building on the south bank of the Thames, directly across the river from the Houses of Parliament. The architect was Ralph Knott, and the building was officially opened in 1922. Look at it from the riverside later and you will see a long curved colonnade facing the water. It was designed to look important, and that was entirely the point.

For most of the twentieth century, this was where London was governed. First the London County Council worked here, and later the Greater London Council. Officials planned housing, schools, roads, and the fire brigade from these corridors. The building faced Parliament across the water, and the two did not always agree. In the 1980s, the council famously hung large banners from the building, aimed squarely at the politicians on the opposite bank.

That rivalry ended in 1986, when the Greater London Council was abolished. The great building stood partly empty for a time, and then it was sold. Hotels, restaurants, and attractions moved in. In 1997, the London Aquarium opened in the lower floors. So here is something many visitors never realise — you are walking through tanks of sharks and rays in the basement of what was once the seat of the capital's government.

In 2008, Merlin Entertainments took over the aquarium and rebranded it as Sea Life. Sea Life is a group of aquariums found in many countries, and each one follows a similar idea. The route leads you on a journey through different waters, from shallow coasts to the open ocean and the frozen south. The displays also carry a steady message about protecting the sea. You will notice it in the signs about plastic waste and overfishing.

The path through the aquarium mostly runs one way, so you can relax and let it carry you. Notice how the light changes from zone to zone. In some rooms it is bright and greenish, like sunlight through a rock pool. In others it turns deep blue, then almost black. These shifts are deliberate. They help you feel the depth of the water, even though you are only a few metres below a busy London street.

Then comes a moment many visitors remember. In one section, the floor turns to thick glass. Beneath your feet, sharks glide through the water. Most people pause at the edge, just for a second. Your brain knows the glass is safe, but your body is not quite so sure. Children often lie flat and press their faces to the floor. Take a moment yourself. Stand still and watch a shadow pass directly under your shoes.

The sharks here are worth a closer look. Watch how they move — constantly, smoothly, rarely stopping. Here is a detail most people miss. Unlike most bony fish, sharks have no swim bladder, the gas-filled sac that keeps other fish afloat. Instead, many sharks rely on a large, oily liver to help with buoyancy. Their skeletons are made of cartilage, the same flexible material that shapes your nose and ears, not bone.

Now find the rays. They ripple through the water like moving blankets, and sometimes they rise up against the glass. When one does, look at its pale underside. You will probably see what looks like a smiling little face. It is a lovely illusion. Those two "eyes" are actually nostrils, and the "smile" is the mouth. The ray's real eyes sit on the top of its body, looking upward, well away from the sand where it feeds.

Further on, the air feels colder, and you reach the penguins. These are Gentoo penguins, a species from the cold Southern Ocean. You can recognise them by their bright orange bills and a white patch that runs across the top of the head, like a little headband. On land they waddle and look slightly clumsy. Under water, everything changes. Gentoos are often described as the fastest swimmers of all penguins, and you can see why as they shoot past the glass.

Keep an eye out for the jellyfish too. In their tanks they pulse slowly under soft light, almost like breathing. They are older than the dinosaurs as a group, and they manage life without a brain, a heart, or bones. Their bodies are mostly water. It is strange to stand in a building once full of planners and committees, and look at a creature that has survived for so long with no central control at all.

As you walk, listen to the people around you. You will hear school groups counting fish, toddlers shouting at turtles or sharks, and couples speaking in low voices in the darker rooms. Staff members appear at certain points to give talks or feed the animals. If you hear a small crowd gathering, follow it. Feeding moments are often when the animals are most active, and the keepers usually share a story or two about individual creatures.

It is worth thinking about the river that runs just outside these walls. The Thames was once so polluted that it was described as biologically dead in parts. Today, seals, porpoises, and many fish species have returned to its waters. That recovery took decades of cleaner sewage systems and careful work. It gives the conservation message inside a real local shape. The sea is not far away. It starts at the river beside you.

When you climb back up into daylight, give your eyes a moment to adjust. The noise of the South Bank returns — buskers, footsteps, the distant rumble of traffic on the bridge. Turn and look at the stone face of County Hall, with its curved columns facing Parliament. Then look down at the brown Thames moving past the wall. Somewhere below your feet, the sharks are still circling, quiet and patient, in the basement of an old town hall.