Requirements: the chests will be received by players level 15+
To access the event, click on its icon in the right-hand menu:

The event window looks like that:

In this event, you need to open chests.
There are 45 chests altogether, and you will receive rewards in each of them. Rewards drop on a random basis.

The main reward is the Parthenon, 6x9, can be placed anywhere

There are 3 ways to get Keys:

1. Complete the quests.
The quests appear in the left-hand menu one after another:

Christmas dinner I (3 keys)
Ask friends for 5 repair kits
Collect 9 reinforcements (Cargo Port)
Collect 7 screw wrenches (drop in your friends’ cities)

Christmas dinner II (3 keys)
Collect 8 pumps (Water Tower, Upgraded Water Tower)
Collect 21 jugs (Bakery, Upgraded Bakery)
Collect 16 valves (Premium cottage)

Christmas dinner III (4 keys)
Collect 6 books (School, Valley School)
Collect 17 maps of the stars (Stationery Shop, Upgraded Stationery Shop)
Collect 7 dandelions (drop in your friends’ cities)

2. Collect profits from the following buildings:
Supertanic: 1 key every 24 hours
Windmill: 1 key every 18 hours
Church of St Mary: 2-3 keys every 24 hours
Villa Masini: 2-3 keys every 24 hours
Pavilion Hanau: 2-3 keys every 24 hours

Villa Masini, 7x6, can be placed anywhere