The land to the right of the Gateway of Luck and behind the castle requires level 7 and 250 gold (I have not reached level 7 as of yet). But the land to the left of the gateway requires level 5 and 125 gold, so this is the route that I am purchasing.
Now we can see the requirements for getting the Gateway of Luck land plot... level 7 and 250 gold.
Once you've gotten 250 gold and level 7 by selling to Myra and exploring the Ancient Watchtower, purchase the gateway land.
The Gateway of Luck allows you to send two heroes in. You will need 1 ladder and 1 torch, but you get 50xp for each hero you send in. There is also a chance you find a silver vault hinge, jade clover, midas glove, and a very low chance of finding a golden vault padlock.