In a medium glass or stainless-steel bowl, combine 3 cups of the bread cubes with the vinegar. Add the water; set aside 5 minutes to soften.
In a blender, combine the cucumbers, onion, almonds, 1 clove of the garlic, and 1 cup of the grapes. Add the soaked bread, the 1/2 cup olive oil, and 1 teaspoon of the salt. Puree until smooth. Put the soup in the refrigerator to chill for about 20 minutes, or up to several hours.
Meanwhile, in a large nonstick frying pan, heat the remaining 2 tablespoons of oil over moderately high heat. Add the shrimp and the remaining 1 clove garlic and 1 teaspoon salt. Cook, stirring frequently, until the shrimp are just done, 3 to 5 minutes. Remove the shrimp with a slotted spoon.
Reduce the heat to moderate and add the remaining 3 cups of bread cubes. Cook, stirring frequently, until the bread is crisp and golden, about 5 minutes.
Cut the remaining grapes in half. In a small bowl, stir together the halved grapes, the shrimp, and the croutons. Serve the gazpacho (thinned with a small amount of water if it's thicker than you like) topped with the warm or room-temperature shrimp-and-grape mixture.
Recipe reprinted by permission of Food and Wine. All rights reserved.