If you're feeling adventurous, go to Bar Marsella for its specialty: Absinthe (absenta). Picasso and Dalí may have been regulars here and it looks like they haven't dusted the bottles since. The bar's said to be Barcelona's oldest and has been around since 1820, serving the homemade drink that's made the place famous. Absinthe is an impossibly strong, aniseed-tasting concoction (the bane of Vincent van Gogh, among others) made, in part, with the herb wormwood. Some countries ban it for its alleged hallucinogenic qualities, which led to it being called "the green fairy." Here they serve it the traditional way: With a fork, a small bottle of water, and a sugar cube. Place the sugar on the fork prongs, and balance it over the rim of your glass. Then slowly drip a little of the water (not too much!) over the sugar so that it slowly dissolves into the drink. Wait for it to sink in, and then keep adding drips of water so that the sugar has nearly all dripped into your glass. Then mix the last of the sugar into your glass with the fork, and drink. One glass won't do you much harm, but you can see those around the bar who've had at least a few by their glassy expressions and loose jaws.