|The government offices. Not much to look at, considering all the pain involved in unlocking it.|
The base Cities: Skylines game doesn't have similar disasters. There's an expansion coming that adds them, but until then, your city is safe from floods and storms. But that doesn't mean there's no incentive to wreck what you've built.
There are a variety of unique buildings available to unlock, based on reaching certain thresholds in city statistics. Many are positive, such as acquiring a large amount of cash reserves or building large areas of residential buildings. Others, though, aren't so good for your city: go into debt, pile up garbage across the city, have low citizen heath, and so on. Sickness and garbage aren't as flashy as earthquakes and floods, but they can bring a city to its knees.
I recently decided to try for the Government Offices unlock, which requires that the average building in the city have 40 units of garbage piled up. That's well above the threshold at which people get angry, so I knew nothing good would happen. Cities: Skylines allows you to control your city service buildings, so I disabled all the garbage collection services. (Which is much better than destroying them, since you don't have to pay to rebuild later.) Sure enough, before long my city was awash in both garbage and unhappy citizens.
By the time the garbage had piled up to the point where the Government Offices unlocked, a lot of citizens had fled the city. Couldn't handle the smell, I assume. That left a lot of abandoned buildings, which coincidentally unlocked the Cathedral - 2000 abandoned buildings maintained across five weeks of game time. Two unique buildings in the same self-inflicted disaster!
It's a good thing you can pause the game, because there were a lot of abandoned buildings to clear out. I spent the better part of a half hour scrolling across the entire city, bulldozing building after building. Then I had to go back and make sure that the now sparsely populated area was connected properly to power lines, since destroyed buildings no longer transmit power to their neighbors.
It took a while for the land value to recover, so I was busy for quite some time micro-managing the cost of city services and destroying new abandoned buildings when they popped up. Ended up having to take out loans to keep the city finances afloat. Fortunately, people started to move back in before too long, so I could cover the loan payments and slowly start building the city back to its former glory.
Those unique building unlocks are a one-time thing, so if I hadn't managed to pull my city out of its downward spiral, I could have started a new one and still kept my building options. I'm glad I saved this one, though. Adds a little extra sense of accomplishment to the process!