Basically, from what I can figure, today is 초복, the first day of this annual stretch determined by the lunar calendar. In 10 days we'll have 중복, and in another 10 days after that is 말복.
On these days restaurants that serve samgyetang and (to a certain extent) boshintang are filled to capacity. Koreans believe that eating hot, healthy soups on these days are the best remedy to beat the heat. What's the reasoning? Well, basically, we should be eating hot things to bring on the sweat which then leads the body to cool down. And why particularly samgyetang and boshintang? Well, samgyetang is a chicken soup filled with garlic and ginseng. Everyone has probably heard of the supposed health benefits to ginseng. So, boost energy and sweat out the heat together. What about boshintang? Boshintang is dog meat soup. There are many supposed health benefits to eating dog, the main one of which is virility and stamina in men. So, lest you feel tired, go eat some dog. It might perk you up a bit.
Now, myself, I had a big steaming bowl of ramyeon for lunch today. No, there's no health benefits to eating this (especially with a big slice of processed cheese on top) but you'd think, according to this principal of fighting heat with heat, eating a big bowl of steaming hot ramyeon should cool me right down, right? Well, I'm sorry to say that it had the opposite effect on me. Before eating it I was feeling more or less comfortable, but after eating it, I was in a pool of sweat for the rest of the day. Not so comfortable, or cool, especially when air conditioners are not working the way they should be practically everywhere I go.
I did have some school provided samgyetang for dinner a la preschooler's leftovers in the kitchen. It was pretty darn good, but I wouldn't call it cool and refreshing.
Personally, I'd take some patbingsu over steaming hot bowls of soup anytime. :-)