You've seem most of them already, on postcards, on T-shirts, in books. But seeing them for real and for free in one of the most welcoming, friendliest and most beautiful buildings on earth is one of life's better experiences. Every work in Washington's National Gallery of Art is a masterpiece and how that building came to be is an extraordinary example of one man's vision and generosity.
Andrew W. Mellon, financier and art lover from Pittsburg, arrived in Washington to work in the Treasury in 1921. In 1936, when he was 66, he wrote to Roosevelt offering not only to donate his $40m collection but also to fund the building of a national gallery, at a cost of $10m. There's an offer. Millionaires, take note.
Though Mellon died soon after the foundations were dug, the gallery opened in 1941 and now has over four million visitors each year. And the design is genius: concrete, steel, pale pink Tennessee marble, Italian marble, Alabama and Indiana limestone; fountains, greenery and skylights everywhere on its three-acre roof mean that natural light floods the building.
This light-filled painting belongs in this light-filled space. Matisse was 36 when he and painter friend André Derain headed to the seaside at Collioure, a small French fishing port near the Spanish border - and there he made this painting, which opens onto summer but also opens, as suggested by Washington's National Gallery, onto the future of 20th-century painting.
The brightly painted walls frame the glazed, open shutters and draw the eye towards that light-filled, foliage-framed wrought ironwork and flowerpot-filled balcony. Beyond again, the freedom of blue boats dancing on pink waves beneath a pinkish, bluish, turquoise sky, bands of colour that Derain called sticks of dynamite, colours that outraged gallery-goers in Paris at the Salon d'Automne and earned this kind of artists the name fauvism, from the French word for "wild beasts".
It's a happy work - and yet this Matisse painting was laughed at when first shown. But then, artists are always ahead; it is we who have to play catch up. Our response now is pure joy, delight, celebration. And no one's laughing.