Bose–Einstein condensate (Bose–Einstein condensate - Wikipedia) is only B-start cool thing that I can think of. It is fifth state of matter that the temperature very close to absolute zero (< 1 Kelvin or < -272.15 °C). Behavior of matter in that state is also cool 
What is the temperature in the Netherlands now ?
Cold Coconut Milk (or a Caramel Sundae)
peaked at 30 degrees Celsius today… funny enough, it was usually that hot back in the Philippines BUT we had air conditioning at work and at home lol…
D
Dairy Queen. Some ice cream or Blizzards… 
E-start… Ethane Ice Clouds on Titan, the largest moon of Saturn, is the only E-start cool thing that I can think of 
(Reference : http://www.personal.psu.edu/faculty/r/d/rdm5/Titan_Chem_Web_Site/Tholin%20articles/Microphysical_Modeling.pdf)
@sleepyhead Yes, 30 degrees is also a average temperature here in Thailand. In summer, it is hotter than that. And Yes, it is hard to live if there is no air conditioning
F - Frozen Yogurt! nice treat that can be made healthy with fruit/nuts, or unhealthy with candy, chocolate, caramel, syrups…
@u2371 oooh our countries (Philippines, Thailand) are so similar i remember when i was younger, before my school got air-conditioning… I could barely concentrate in the summers haha
Glacier (Glacier - Wikipedia)
The mechanism of how it flow is also cool
@sleepyhead Yes, and the global warming also make it worse
@u2371 ooh tell me about it… the typhoon/monsoon season in the Philippines is shifting already because of that!
H
a cold Heineken beer,
or helado, the Spanish word for ice cream,
or a trip up to the Himalayas!
Ice cream 
or an iced chocolate / coffee drink 
Wait, does
Fit in the topic of…
Else Gelato for G… 
Edit - so to clarify, the topic is…
ways to cool off / or cool as in super or amazing things about the cold…
J next…
I’m inclined to accept glacier, one can visit one to cool off 
not very likely or practical, but it works (and also to set precedent in case @littleKAF forces us to oceans or continents again lol)
Yes, anyone can visit it to cool off 
Jamba Juice.
Kiwifruit ice block or ice cream or chilled kiwifruit works too 
L
Lemonade!
Lime juice too maybe?
Margarita, frozen preferably
N
Negroni, it comes with ice so…
Swim in the Ocean
@sleepyhead …being hot in the Netherlands sounds like experiencing winter in Sydney. We don’t expect it to be cold, don’t heat our houses properly and so feel colder with a Max of 12-14c than living somewhere a lot colder that prepares properly for winter!
P
Going to the Poles, north or south 
No let’s be more practical. Taking a dip in the Pool
@PM229 that’s an excellent point! Here in the Netherlands and in France, houses are built to withstand cold winters… the Philippines is much like Australia, preparing for the heat - with air conditioning and screens on windows so they can be thrown open….
You stole my answer. 
How about Quenching your thirst?
And for a new topic, let’s celebrate our southerners with ways to stay warm in the middle of the winter.
nice new topic
do we jump to it, or continue with this one? I suggested this one but I don’t mind switching
we could continue and finish, then jump to kaffy’s?
R - sticking your head in a refrigerator (or your whole body if it’s big enough!)