Private view: our art critic's favourite online galleries

The world’s great art museums have closed their doors – but you can travel within their walls virtually to see treasures up closeTwo weeks ago, Andy Warhol opened at Tate Modern, then closed again. The artist barely got his 15 minutes. If you need an Andy fix, why not visit the website of the Warhol Museum in Pittsburgh, which has the largest holdings of the artist’s work in the world? If you never got to see the National Gallery’s Titian exhibition (or even if you did),