Utrecht is dotted with special buildings, which you bike past regularly but know very little about. Take the green steel building that recently emerged from behind the mountains of sand on Cartesiusweg. Building work is in full swing along the railway line beside Cartesiusweg. The CAB building is completely fenced off and piles of sand are everywhere. DB’s is even more difficult to see, but will shortly relocate. And rising among the half-finished apartment blocks, foundation pits and dilapidated, soon-to-be-demolished sheds, a bright industrial building made from pale-green steel and glass proudly raises its head. You’d be forgiven for thinking it had always been there, but somehow out of sight. The building is called SOLO. It houses eighty rented apartments and was designed by Zecc, an Utrecht-based architects’ office based in the Werkspoorkathedraal. Solo is currently a good name, but very soon every inch of the Cartesiusdriehoek (as this area is known) will be redeveloped, up to and including a tower on top of the CAB building. So this little green gem will not be alone for long, although it will be the only apartment block to be built in the planned central park. To accentuate its unique position, Zecc rotated the building 90 degrees, while all the other apartment blocks are in straight rows. Steel was chosen as a reminder of Utrecht’s industrial past. But Zecc did not only do this for decorative purposes: all that steel has a function, even the beautiful craftwork above the communal entrance is constructional. This is also the entrance to the bike park, which is partly underground, and leads to a wide staircase giving access to a communal courtyard. A tree standing at a lower level in the ground in the middle of the courtyard will largely take care of itself, and the opening in the floor solved the problem of daylight in the bike cellar. Solo was largely factory built: using a series of prefab elements, it took about a year to construct. The four corners have been rounded off and the concrete supports on the ground floor have a curve, as a nod to the architect Sybold van Ravesteyn, who designed the CAB building. But perhaps the nicest detail in Solo is the transformer house, smack bang in front of the stairs: constructed entirely from green steel; pretentious and rigorous.