At the now widely praised British Library, architect Sandy Wilson created a separate glass tower for the King's Library of George III, which rises up through the great foyer as if extruded from the vaults below. At Lancaster, MacCormac - a one-time pupil of Wilson's - plays the same trick. The heart of the Ruskin collection is expressed as a separate rectangular building, standing free within the oval carapace you see from outside. You walk towards it on semi-transparent paving, part glass, part slate: the inner building seems to spring from the bowels of the earth. It can be completely sealed, but usually some of the plaster panels swing out as shutters, revealing windows behind. The main one of these - which you see from outside through the glazed entrance slot of the oval building - bears a seemingly abstract image by artist Alex Beleschenko. It turns out to be a giant blow-up of a daguerrotype of Venice taken from the archive.

The difference between the libraries in London and Lancaster, apart from scale, is that MacCormac's building within a building is a solid rather than transparent object, clad in panels of rich red Venetian plaster of the kind so loved by Ruskin (Venice was the foundation of all Ruskin's aesthetic theorizing). Within this sanctum is one of the most intense, womb-like architectural spaces anywhere: a deep red meeting room within the box, its tall leather-backed chairs and fine joinery again recalling the vastly bigger reading rooms of the British Library. Here, in contrast, the room is so secretive, so reclusive, as to seem the headquarters of a secret society.

This is perhaps apt. Ruskin's colossal popularity as an aesthete in the late 19th century, when even a brand of cigars was named after him, seems incredible now: he has fallen into the hands of scholars, and there he will most likely remain. Ruskin was a prophet, forecasting the evil environmental effects of industrialisation, becoming a proto-socialist and proto-conservationist (his Guild of St. George anticipated the National Trust), inspiring the pre-Raphaelites, William Morris, the Arts and Crafts movement, and generally jump-starting the whole one-foot-in-the past mentality of the late Victorian era. He will have his revival - the centenary of his death falls in the year 2000 - but he will never regain the intensity of fame that he enjoyed at his peak.