Requirements: level 15+

In this event, you can open chests and receive guaranteed prizes from each of them.
There are 45 chests in total and rewards drop on a random basis.

The main reward is Cologne Central Mosque, size 6*9, can be placed anywhere
Every 24 hours:
4200 coins
1-3 energy
1-3 daffodils (spring) OR  1-3 pearls (summer)

Each chest can be opened with 9 Spring keys
There are 3 ways to get the Keys:

1. Completing quests
Key quests will appear one after the other in the menu on the left side

Old Design School I
Collect 7 Screw wrenches (from buildings in friends' cities; do not drop every time)
Collect  9 Fire extinguishers (Water Tower, Upgraded Water Tower)
Collect 7 Reinforcements (Cargo port)

Old Design School II
Collect 6 Repair kits (ask friends)
Collect 20 Pencils (Stationery Shop, Upgraded Stationery Shop)
Collect  21 Jugs (Bakery, Upgraded Bakery)

Old Design School III
Collect 17 Valves (Premium Cottage)
Collect 22 Pistons (Shoe Shop, Upgraded Shoe Shop)
Collect 10 Spools of thread (Textile Factory - any product, Upgraded Textile Factory - Wool, Felt, Cashmere)

2. Collect profits from certain buildings:
San Carlo alle Quattro Fontane: 2-3 keys every 24 hours
Ateneum: 2-3 keys every 24 hours
Museum of Paleontology: 1 key every 8 hours
Central Station: 1 key every 24 hours
Nobel Prize Museum: 2-3 keys every 24 hours

3. Purchasing keys from a special offer

Unique offer: Nobel Prize Museum, size 8*6, can be placed anywhere

Every 24 hours:
4000 coins
1-4 energy
1-4 daffodils (spring) OR  1-4 pearls (summer)
2-3 Spring Keys  during the promotion