Carthusian complexity.

Guillermo Vazquez Consuegra's rejuvenation of a Carthusian monastery in Seville instils a spatial richness and material refinement to a heterogeneous collection of original buildings.

Seville's La Cartuja, on the island of that name in the Guadalquivir River, was built as the Carthusian monastery of Santa Maria de las Cuevas. A large complex, enclosed with its gardens and orchards by an imposing wall, it became famous because Christopher Columbus stayed there while preparing for his voyages of discovery. Since then it has had a chequered history. Frequent flooding and an earthquake necessitated periodic rebuilding. Napoleon's army occupied it. The monks left in 1835 and it was in grave disrepair when later in the same century a British industrialist converted part of it into the Pickman ceramic works. Colourful glazed tiles associated with Seville were made from the island's clay and baked in tall tapering kilns that now dominate the Cartuja.

More recently, the island was the site of the 1992 Seville Expo celebrating the 500th anniversary of Columbus's discovery of the New World. For this, parts of the Cartuja were renovated to house permanent uses, a process that continues. The latest phase, which remains incomplete, is Guillermo Vazquez Consuegra's conversion of the Pickman works that occupied and surrounded the remnants of the lay brothers' cloister to house the Andalusian Heritage Institute. A prime function of the institute is conserving art works.

On taking the commission, Vazquez Consuegra found himself faced with a tightly-packed jumble of buildings of differing ages, condition and architectural value. Much was fit only for demolition and his first task was to assess what to save. Besides conserving what was oldest, most characterful and accommodating, or in best physical condition, he wanted to retain fragments that tell of the history and functions of the monastery and ceramic works. Yet he also wanted to make room to plan, around ample outdoor space, a coherently-organised complex in which the best remnants from the past could be shown to advantage, whether inside or out.

The institute comprises a series of linked blocks, each housing a different function. Some, like the exhibition and administration block, are converted from the original fabric once newer extensions were cleared away. Others, like the unbuilt research and education block, will be almost entirely new. And others, like the restoration studios, were completely rebuilt within old outer walls.

The Cartuja complex is entered by a ceramic-tiled gate. If instead of proceeding down the lane that extends straight ahead to the west, you turn sharply to the north-east you find yourself in a courtyard. Here institute staff park their cars below a tiled roof against the boundary wall. This roof meets another that sweeps down, over an escape stair, from a higher roof. The floating roofs and their spindly steel supporting structure are really simple, but thrilling nonetheless.

Across from the parking is a roofed loading bay. Ahead the staff entrance leads into the corner of an L of long, narrow open spaces. The route straight ahead is flanked on the right (east) by workshops and will lead to the research and educational block. This will have laboratories on the ground floor and lecture theatres on the first. The other open space extends left and Westwards below a vine-clad pergola that recalls the double-pitched roofs that once covered it and most of the other spaces. It is now a pleasant outdoor seating area for the staff cafeteria that edges its far side.

On its opposite side the cafeteria overlooks, through a long horizontal window set at water level, the tanks where the clay was once mixed. These occupy a quadrant of what will be a patio between the cafeteria and the research and education block. The open ground floor of a wing of this block will connect this patio to a larger one, across which are visible remnants of the arcade of the lay brothers' cloister.

The public entrances are reached by proceeding straight ahead from the gate into the Cartuja, past the southern wall of the restoration studios. Beyond these, an old archway, crossed by a new glazed-in bridge, opens into a lane that leads northwards to what was the main entrance of the Pickman works. To the left of this is a door into an entrance hall, with a rather pompous symmetrical stair, which is also entered from the grounds to the west. Extending from this hall are exhibition galleries which show off the original fabric. The one to the south has a vaulted ceiling; and the northern one has brick arches on the long sides of a central well which brings natural light down through the floor above.

As with much other new construction, the structure on this upper level is fair-faced concrete. Within this, wooden partitions and a raised floor create a suite of administrative offices. These surround the light well, taking natural light from windows overlooking the gallery below and from an internal clerestory set between the slotted ceiling of the well and the ventilated rooflight that crowns the ridge of the tiled roof. Above the southern, vaulted gallery is a library reading room.

Although most books are stored elsewhere, glass-fronted bookshelves line the walls between the tall windows. The central strip of the ceiling is open to reveal the roof structure and is edged by perspex strips through which the room is artificially lit. The ceiling and linings that lean in from the windows to conceal air-conditioning ducts are in coarse-grained chipboard of the same colour as the oak strip floor. The bridge across the arch into the entrance lane connects the room's south-east corner with a gallery (used for documentation) in the southernmost restoration studio, and via this with the bookstacks. These fill the three floors of a retained building, the shelves lining the walls and forming semi-circles around a circular central well.

The four restoration studios are lofty, serene and handsome. Each has a curving concrete roof that rises to a tall north-light clerestory. The glazing of these is conspicuous outside as it projects forward from and back over the slotted northern edges of the concrete roofs. Thus shafts of direct sunlight animate these bright-lit spaces where artworks are not stored but worked on painstakingly. East of these workshops is a broad corridor that links them to each other and the loading bay. Beyond the corridor is a photographic studio.

Typically of this architect, his interventions are shaped by his sure sensibility rather than by any rigorously consistent strategy. Some may see the results as overly episodic. But consistency is too often reductive. The approach applied here suits admirably the heterogeneity of both what was retained and the functions accommodated. Each of the institute's linked blocks is quite distinct yet apposite in character. The result is a work of considerable spatial richness and inventive but always refined detail.