Towner Gallery, Eastbourne, UK

The Victorian resort towns on Britain’s south coast were hit hard by the arrival of cheap overseas holidays. For more than a generation, these towns were abandoned to pensioners. Their streets are lined with the kinds of coffee lounges and mangy boutiques that have long disappeared elsewhere; their superb architectural infrastructure – piers, grand hotels, promenades and bandstands – flakes and rusts in the salty air. Then, a couple of years ago, the restoration of Bexhill’s De la Warr Pavilion, the finest modernist building in Britain in the most unlikely of settings, suggested a future for tourism beyond chips, coaches and ice-cream cones. It was followed by an excellent Triennial and a new gallery in Folkestone; Hastings looks likely to get a building to display the Jerwood Foundation’s collection; and the latest instalment is Eastbourne’s £8.6m Towner Gallery, designed by architect Rick Mather.

Stuffed away behind a fine, solid modernist theatre from 1963, the site is unpromising. Yet in a world of attention-seeking arts buildings, the Towner’s façade is a painterly composition, a monochrome abstract that melts into its glass and concrete neighbour by day but glows in the evening. It reveals an open lobby and shop that appears as an extension of the street and, with no fuss, visitors are propelled into the ground floor galleries. Shared with the theatre and convertible to conference use, these rooms are big, spacious and loose, expressed in white and raw concrete.

As one rises, in a large elevator or on a simple steel stair, the first-floor galleries are useful but unspectacular. They are, however, well filled with the Towner’s admirably coherent collection, which focuses on the land and seascapes of the south coast and embraces art by Eric Ravilious (of whose work it has the finest collection), Christopher Wood, William Nicholson and Duncan Grant.

The site faces away from the sea in a dip on a dull suburban road. But Mather has oriented it towards the South Downs so the chalk cliffs that define both the surrounding landscape and the art on the walls root the building in its location. The crests of the Downs are glimpsed through circulation spaces and even from the elevator, while the café lifts the sparse interior above neo-vernacular brick dullness.

The building is crowned by a second-floor gallery that is as fine as an artist or curator could ask for. Lofty but not too tall, crisply detailed but rough and understated enough not to detract from the art, it is shown off wonderfully by the current exhibition of work by Chilean artist Iván Navarro. Fluorescent tube characters line the walls, imitating Otl Aicher’s memorably minimal pictograms for the 1972 Olympics and illuminating the gallery curiously, almost spotlighting it from below to bring the ceiling into sharp focus.

But, while it is a superb volume, a space that echoes the Kunsthalle model of Germany and Switzerland, I am astonished by the lack of natural top light in a gallery that sits above the building. I am sure it is easier to control lights with a switch but the coast seems to me so dependent on its changing light that this is an inexplicable omission. Another jarring problem is the hideous curving façade that wraps round the far side of the building. Its random, deep openings seem to want to recall Le Corbusier’s chapel at Ronchamp but the papery thinness of the render makes them instead like bad developer’s moderne.

Mather achieved something similar to the Towner with his extension to the Lyric Theatre in Hammersmith, London – an intelligent, pared-down modernism, sympathetic to a slightly ugly neighbour, urbane, robust and good value. At Eastbourne, he has built a gallery as contemporary and broadly enjoyable as the iron and glass seaside concoctions of the seafront were in their day.