Torre de Collserola

Find the ridge line to the north. Above the city's rooftops, the hills of Collserola form a long green wall. On that wall, one slender shape stands out. It is a thin grey needle, held in place by cables that catch the light like fishing line. On a clear morning it looks almost weightless. This is the Torre de Collserola, and from the streets of L'Hospitalet you can often see it watching over the whole plain of the Llobregat.

The tower does not stand in L'Hospitalet itself. It rises on the Collserola ridge above Barcelona, near the summit of Tibidabo. But from this side of the metropolitan area, it is one of the clearest landmarks on the skyline. Many people here use it the way sailors use a lighthouse. If you can see the needle, you know which way the mountains are. And if you know the mountains, you know which way the sea is.

So what exactly are you looking at? The Torre de Collserola is a telecommunications tower. It carries television, radio and other signals across Barcelona and the surrounding region. Its total height, including the mast at the top, is 288 metres. Because it stands on a hill that is already high, the tip of the tower sits far above the city. That is why it appears on the horizon from so many neighbourhoods, even ones several kilometres away.

The tower opened in 1992, in time for the Barcelona Olympic Games. That year changed the city. New ring roads, a rebuilt waterfront, new sports venues and new infrastructure appeared in a short burst of work. The Games needed to reach a global television audience. A modern broadcasting tower was part of that plan. Before it existed, the ridge was crowded with many separate antennas and masts. One of the goals was to gather much of that equipment into a single structure.

The design came from the office of the British architect Norman Foster. His team is known for buildings that show their structure openly. Here you can see that idea very clearly. Most broadcasting towers are wide, heavy columns of concrete. This one is different. The concrete core is surprisingly narrow — closer to a lamp post than a castle. Almost everything that keeps it upright happens outside that core, in plain view.

Look for the cables. Long lines of tensioned steel run down from the tower to anchors in the hillside. They work like the guy ropes on a tent. They pull in three directions and keep the slim shaft steady against the wind. From far away the cables almost disappear. Then the sun moves, they catch the light, and suddenly the whole system appears as a fine triangle of lines. It is worth watching the tower for a few minutes just to see that change.

Here is a detail most visitors miss. Higher up, the cables are not ordinary steel. The upper section uses non-metallic fibre cables. Metal near the antennas could disturb the signals the tower sends out. So the engineers chose a material that is strong but does not interfere with broadcasting. Something that looks like simple rigging is in fact part of the radio design.

About one third of the way up, the tower widens into a stack of platforms. They hold the equipment, the antennas and the technical rooms. Seen from below, they look like a set of discs threaded onto the shaft. Their shape has a soft, triangular outline, and the edges are wrapped in metal grilles. Above them, the thin mast continues upward and tapers into the sky. The top carries a red warning light for aircraft, which you can see at night from far across the plain.

The tower is not only for machines. One platform holds a public viewing deck, and a glass lift carries visitors up the outside of the shaft. As the lift rises, the hillside drops away and the city opens below. On a clear day the view runs from the Mediterranean to the Pyrenees foothills. You can trace the Llobregat delta, the airport, the port cranes, and the dense grid of the Eixample district in central Barcelona.

The project was not welcomed by everyone. When it was planned, some local groups and environmental campaigners objected. Collserola is a large natural park, a green lung between Barcelona and the towns of the Vallès. Critics worried about building a tall structure on a sensitive ridge. Part of the answer was the slim design itself. A thin shaft with cables puts far less weight and concrete onto the mountain than a massive tower would.

The neighbourhood around the tower is unusual too. A short distance away stands the Tibidabo amusement park, one of the oldest in Spain, with its old rides perched on the summit. Next to it rises the Temple of the Sacred Heart, a church topped by a large statue of Christ. So on one ridge you have faith, fairground and broadcasting side by side. From L'Hospitalet you can sometimes pick out all three along the skyline.

The park itself is worth a moment of thought. Collserola covers thousands of hectares of pine and oak woodland, with walking trails and old farmhouses. Wild boar live in these hills, and they sometimes wander down into the edges of the city at night. The tower stands above all of this. It is a piece of high technology surrounded by forest, and the contrast is part of its character.

Now look back at the ridge. Notice how the tower changes with the weather. On hazy summer afternoons it fades into a pale shadow. After rain, when the air is clean, the cables and platforms become sharp and close. At dusk the red light at the top switches on, a small point above the darkening hills. It is the same structure every day, but it never looks quite the same twice.

As you move on through L'Hospitalet, keep glancing north. Between tall apartment blocks and over the railway lines, the needle will appear and disappear. It is a quiet companion to the city — a signal tower that most people pass without thinking about. Now you know a little of what it carries, and how it stands. Next time it catches the light, you might stop for a second and look.