What is the meaning of “What a box to sweat in!”？

I have started to read "The Sun Also Rises" by Ernest Hemingway. I stumbled a lot shortly after the beginning, as I'm a middle-aged Japanese dude who is struggling to learn English. I need someone's help.

The first problem is the meaning of the sentence “What a box to sweat in!”. It occurs in the dancing scene.

The context is as follows: 

"It was hot and we came off the floor perspiring. “My God,” Georgette said. “What a box to sweat in!”".

I can guess why Georgette exclaimed that it was so hot. But what is "a box"? Is that the dancing room or the floor? What is "to sweat in"? What is the object of the "in"?  Did they "sweat in a box"? I can't get the nuance.

Thank you in advance for your help. Any comments and/or corrections on my questions are also welcomed.

Solution 1:

There is such a thing as a sweatbox, which Oxforddictionaries.com defines as follows:

1 A confined space in which one or more individuals are punished or tortured with conditions of extreme heat and dehydration.

2 A heated compartment in which perspiration is induced, to encourage weight loss, pore cleansing, etc.

The online Merriam-Webster dates the first appearance of the word to 1864, and includes a further sense of the word as

2 : a device for sweating something (as hides in tanning or dried figs)

So Georgette's exclamation is an oblique reference to a sweatbox; which sense of the word is uppermost in her mind at this point, I cannot say. Perhaps it's a bit of each.

Solution 2:

"What a box" is describing the room they were in. It is like a box, so it is presumably small, plain, and not very well ventilated.

Hemingway had a very economical style of writing, sometimes described as "The Theory of Omission" and sometimes as "The Iceberg Theory". The general idea is that if the writer knows something, and the reader knows it too, there is no need to actually say it. He likened this to an iceberg where we see only one eighth of it, and the rest is out of sight but we know it is there.

One technique he used to achieve this was to use one thing to describe another, and this can be seen in your quote. Instead of describing the room for the reader - "The room was small, plain, and square with no windows or ventilation, and it felt like being in a box" - he use the character Georgette to comment on it - "What a box". As Hemingway considers that we all know what a box looks like, he doesn't describe any further. Those three words are all he needs. Saying it is a box is the one eighth of the iceberg; the readers knowledge of what a box is like provides the rest.