The Observatory is a level 4 unique building that you can build in Cities: Skylines. To unlock it, you must have 1,000 abandoned buildings in your city for 5 weeks. You’ll also need to reach the Busy Town milestone (8,000 – 36,000 population, depending on the map).
Once these requirements are fulfilled, you’ll be able to build the Observatory from the level 4 tab of the Unique Buildings menu for ₡85,000. Until then you can hover over its silhouette in the menu to see your progress towards the unlock.
Note: Do not confuse the Observatory for the Observation Tower, a level 5 unique building that requires the Park Life DLC.
The Observatory is a requirement for the Fusion Power Plant monument.
Tip: Create a Restore Point
This is a very destructive unlock requirement, so you likely won’t want to deal with its lasting effects in your city (especially since you’ll need a fairly large city to begin with in order to have 1,000 abandoned buildings).
Not only will your population plummet, but so will your economy.
Depending on how large your population is, you’ll want to have a few million in your bank account to make sure you don’t go bankrupt before you finish unlocking.
To spare yourself the headache of having to recover from this, create a save point of your “good city” that you can revert to after you’ve trashed your city for this unlock.
Step 1: Create a save point of your largest city. Add “before abandoned” or something to the savefile name so you’ll know which one it is.
Step 2: Make sure that autosave is off (Options > Gameplay).
Step 3: Proceed with the unlock.
Step 4: Do NOT save over your file. Close the current game and reload to the save point you created earlier. You should still be able to build the Observatory from there.
This works because once you unlock a unique building, it stays unlocked across your other saves.
Getting 1,000 Abandoned Buildings
Now that you have a city that you’re ready to destroy, you have a few options for getting people to abandon their homes and workplaces.
- Turning taxes all the way up to the maximum
- Switching off the power
- Switching off or disconnecting their water supply and sewage treatment
- Turning off (or cutting the budget for) the fire, police, and garbage departments, and waiting until your city is overwhelmed by fires, crime, and garbage pile ups
- Turning off all health services, including deathcare, to allow disease to spread (the buildings will be abandoned when the dead bodies are not collected)
You can combine these different methods in order to make more people leave as soon as possible.