In The Great Gatsby by F. Scott Fitzgerald, where do Nick and Gatsby go on "almost the last, certainly the warmest" day of the summer? Who else...

First, Nick and Gatsby go over to Tom and Daisy Buchanans' house in East Egg.  In addition to Nick, Gatsby, Tom, and Daisy, Jordan Baker is also there.  They all spend some time at the house, but it is so incredibly hot that Daisy, especially, feels anxious, and she says, "'everything's so confused.  Let's all go to town!'"  Tom grabs some liquor, and the party leaves.  Tom, Nick, and Jordan all go in Gatsby's car,...

First, Nick and Gatsby go over to Tom and Daisy Buchanans' house in East Egg.  In addition to Nick, Gatsby, Tom, and Daisy, Jordan Baker is also there.  They all spend some time at the house, but it is so incredibly hot that Daisy, especially, feels anxious, and she says, "'everything's so confused.  Let's all go to town!'"  Tom grabs some liquor, and the party leaves.  Tom, Nick, and Jordan all go in Gatsby's car, and Daisy and Gatsby go in Tom's car. 

It is on this trip that Tom learns of George Wilson's plan to take his wife, Myrtle (Tom's mistress), west as a result of learning that she's been having an affair.  It is also during this trip to New York City that Tom reveals Gatsby's status as a bootlegger to Daisy, causing her to second-guess (and eventually abandon) her relationship with him.  Finally, it is on the way home from NYC that Daisy hits Myrtle while driving Gatsby's car, and she ultimately allows Gatsby to take the blame for it.  George's belief that it was Gatsby who'd been sleeping with his wife and killed her with the car led him to shoot Gatsby and then himself.