Go to the Backyard Battleground
Go to the Quest Board
Complete the quests to earn a recommended 15 stars for other trophies (though you only need 5 for this trophy)
Watch the video to see a secret room in the sewers and obtain two Epic Items.
On the docks at the harbour (far middle right-hand side from the Plants perspective) will be some rubble to clear for five stars, clearing the rubble will allow you to put the giant statue or lighthouse (as well as others I don't know how to obtain) up for the trophy.