The best comes last. With major Lottery-funded arts projects on hold for years to come, two of Britain's finest architects, Sir David Chipperfield and Eric Parry, have just delivered a pair of superb art museums: The Hepworth in Wakefield, a town absolutely determined to join the arts big league, and the extended Holburne Museum in Bath, a city which did its very best to scupper the project.
The Hepworth, named after the sculptor Barbara Hepworth, who was born in the city, is the largest British art museum to have been built since Tate St Ives in 1993 – and its art spaces are wholly superior to the Tate's. Some will find the external appearance of the £35m Hepworth dour and "difficult". It's as compellingly stark as the great Sigurd Lewerentz's last building in 1969, the florist's shop at Malmo cemetery. It could also be a Cubist compaction of huge grey cardboard boxes; or a supersized fragment from Paul Klee's painting Dream City, wedged into the bank of the Calder river. The museum's ten irregularly shaped and ridged segments, pressed tightly together, can be read more obviously as an architectural abstraction of the rooflines and perspectives of the 19th-century mills that loom just south of it.
"We wanted to convey three-dimensionality," says Chipperfield. "We set ourselves the task of seeing if the building could be a complex form, and how we could give rigour to it so that it wouldn't just be [wilful] shape-making. It was a puzzle that was difficult and fascinating. It's an innocent enough idea but, to be honest, it was a nightmare... You need spaces that are sufficiently interesting, but not too interesting. Art is not about neutrality."
The Hepworth's concrete shell sits firmly in place by the debris-clotted weir where the Calder swirls into rabidly lathered pools alongside the museum, before sweeping under the dual carriageway past the obdurate sandstone Chantry Chapel, pictured in JMW Turner's 1797 watercolour, Wakefield Bridge, and restored by George Gilbert Scott in 1839.
From inside the museum, there are precisely framed views of Wakefield. If you require a hermetic, world-shut-your-mouth art experience, go elsewhere. The museum, the town, and the substantial Hepworth, Gott and Wakefield municipal art collections come as an open-handed cultural package designed to attract £350m in investments to the town's Waterside regeneration zone. Chipperfield believes that you should be able to approach a building and sense the character and arrangement of the internal spaces. His practice sketches and models its forms, and he talks of outer surfaces pushing back against internal spaces as they take shape, and then striking a final balance.
Gazing into carefully lit 1-to-30 scale models of the galleries allowed his design team to sense hefts and tensions of space and light, producing a narrative of marvellous grace at the Hepworth. The almost baroque qualities of light and shadow in relationship to the changing volumes of space are not obtrusive, but have produced exquisite conditions for the artworks. Chipperfield is not known for strange architectural angularity; and yet, here, fractious geometry has been tamed and civilised to produce one of the finest contemporary art museums in Europe.
The Hepworth's director, Simon Wallis, has mounted important modernist works from the collections, followed by physically and conceptually provocative pieces by Eva Rothschild. This is not going to be a place of neutral encounters with art. Wallis, and Wakefield Council's key Hepworth-boosters, John Foster and Peter Box, are to be congratulated.
Meanwhile, in the grand city of Bath, regiments of Blimps and Pooters are choking back their bile. The re-opening of the £11.2m Holburne Museum of Art, extended and internally remodelled by Eric Parry, has created a uniquely atmospheric cabinet of curiosities in Sydney Place. Yet Bath had been poised to let the Holburne, and its 18th-century hoard of fine art, moulder into terminal disuse rather than agree to Parry's design, considered by many to be an act of architectural terrorism.
According to Parry, the local conservation officer told him: "Lose your dream." One can only assume that this conservation officer prefers another kind of dream: pastiche and depressing heritage dentistry such as the flaccid, Georgian-style facade of the local Debenhams. Architecture like this
turns our town and city centres into Disneyfied and eerily vacuous chunks of Heritage plc radiating the sickly-sweet smell of cultural mortuaries.
But make no mistake: the extension and internal changes at the Holburne represent a daring and debatable architectural intervention. The Holburne had been historically constipated, architecturally. The building was originally designed and built by Charles Harcourt Masters in 1796 as the grand Sydney Hotel, almost opposite Jane Austen's home in Sydney Place. The front of the hotel looked down Great Pulteney Street, one of Bath's finest vistas; and its back – with a terrace, musicians' balcony and supper booths on the grass – faced Sydney Gardens.
Sir Reginald Blomfield remodelled the building between 1913-16 as a classically mannered museum containing Sir Thomas William Holburne's 4000-item collection of 18th-century Old Master paintings, works by Gainsborough, Stubbs and Zoffany, bronzes, maiolica, silver, furniture and miniature portraits.
By restoring the visual axis between Sydney Gardens and Great Pulteney Street, Parry has unlocked what he refers to as the two-faced Janus character of the building and its setting: light and dark, in relation to its north-south axis; town and nature, in relation to the city on one side and the park on the other. The garden, and the view down Great Pulteney Street are, for the first time, staged from within the museum.
Parry's beautifully engineered extension, in super-clear glass and spatter-glazed ceramic tiles, inverts the architectural layering of the original building, which is heavily rusticated at its base and more refined as it rises. The extension's bottom third is transparent, the middle third layered and semi-transparent, and the top third is a solid ceramic box. "True ease in architecture," to paraphrase the Georgian poet, Alexander Pope, "comes from art, not chance." Parry has responded with modernistic artfulness to Blomfield's classical artistry.
The extension will be seen as how-very-dare-you pretension by some, and deserving of a thorough public horse-whipping outside Debenhams. But Parry has achieved a finely-wrought balance between subtlety and surprise. The extension's side elevations, facing more or less east-west, are either in shadow or direct sunlight. In the first condition, the glass and the green-bronze glaze on the ceramic dissolves into sylvan reflections and brindled brushstrokes of shadow and soft, dark colours. In sun, the ceramic becomes surreally vivid.
Inside, Parry has created simple and logical connections between new and old spaces, doubling the museum's exhibition and public space. The two front galleries retain their high-ceilinged grace, and there are three new floors in the extension. The lower pair are highly atmospheric and Soane-like. The only question-mark relates to the new top gallery: the light is rather cold and grey.
Bath now has what it originally didn't want, and will surely learn to love. The architecture of the Holburne is an important blow against witless pastiche in a city that needs new kinds of beauty. Bath's reactions to the Holburne will be watched closely by the creators of the forthcoming firstsite visual arts centre in Colchester – absolutely the last big Lottery-funded arts project. That town, too, has yet to fully realise the civic and human value of innovative artistic ambition.
Eva Rothschild: Hot Touch, The Hepworth, Wakefield (01924 247360) 21 May to 9 October; Peter Blake: A Museum of Myself (to 4 September) and Gainsborough's Landscapes: Themes and Variations (24 September to 8 January) Holburne Museum of Art, Bath (01225 388588)