How do I get the "What the...?" achievement in Cities Skylines?
Solution 1:
This was interestingly hard to find since usually achievement guides are all over the place. However, according to this Reddit post you have to experience a "Chirpnado".
According to Reddit user wasmic:
It's the chirpnado. It has a very, very low chance of occuring. 3/703 - or 0.42 % - of all disaster will be chirpnados.
I wasn't able to find exactly what this disaster will do but, keep a look out for tornadoes sporting little blue birds.