Getting lost in Venice is a cinch: all those labyrinthine, watery alleys. It's something else entirely to lose yourself in Venice and find that you have arrived in a dusty corner of Istanbul. This, however, is exactly the experience Mike Nelson, the first installation artist to officially represent Britain at the Venice Biennale, has created in the British Pavilion.

Nelson is known for labyrinths of his own: his installation The Coral Reef (2000) is a Kafkaesque nightmare of multiple entranceways and foyers that lead nowhere. It's no surprise, then, to find that he has transformed the grand British Pavilion into a series of dark, disorientating spaces.

The floor is thick with dust and dirt, the light switches caked in grime. This is a part-recreation of one of Nelson's previous projects, a reconstruction of a 17th-century caravanserai building created for the 2003 Istanbul Biennial. Stumble into a red dark room and you'll find photographs of Istanbul, but they could be Venice.

There is a knock-out moment when you find yourself in an open Istanbul courtyard, utterly transported. Two almost identical chapel-like rooms, lit only by skylights covered in greenish grease, intensify the sense of doubling: of cities, of east and west. In another room two chandelier shapes hang above a pile of dirty chandelier glass fragments. Two centres of light, craft, power and trade – beautiful ruins all.