The main reward is the Chi Lin Nunnery (4,100 coins, 1-3 energy, 3-4 daffodils every 22 hours, size 9*8, can be placed anywhere)

Each chest can be opened for 7 Easter keys.

There are 3 ways to get Keys:

Completing the quest:

Tidying the Laboratory I
Collect 31 Feather Dusters (Shoe Shop, Upgraded Shoe Shop)
Collect 33 Stepladders (Convenience Store, Upgraded Convenience Store)
Collect 9 Pirate Bandannas (Pub, Upgraded Pub)
Tidying the Laboratory II
Collect 5 Barographs (School, Valley School)
Collect 9 Sensors (Water Tower, Upgraded Water Tower)
Ask friends for 7 Cups of Chamomile tea
Tidying the Laboratory III
Collect 17 Planks (Cargo Port)
Collect 11 Nails (Randomly from friends’ cities - buildings with a clock or coin)
Ask friends for 7 Hammers

2. Collect profits from the following buildings:

Rotunda of Mosta - 2-3 keys every 22 hours;

3. Use the sale offer!

Rotunda of Mosta: 3,700 coins, 1-3 energy, 2-4 daffodils, 2-3 Easter keys during the Chi Lin Nunnery chest event, 150 marathon points one time when buying;
Bremen City Hall: 3,900 coins, 3-4 energy, 2-5 daffodils, 2-4 Easter Keys during the Chi Lin Nunnery chest event, 150 marathon points one time when buying;
Prabhupada's Palace of Gold: 3,600 coins, 2-4 energy, 2-3 daffodils, 1-4 Easter keys during the Chi Lin Nunnery chest event, 150 marathon points one time when buying;
Basilica of the Sacred Heart: 3,700 coins, 2-3 energy, 150 marathon points one time when buying;
Memorial Church: 4,300 coins, 3-5 energy every 20 hours, 80 marathon points one time when buying;
Round Church: 3,400 coins, 2-4 energy every 16 hours.