The lost city is another not-so-difficult world (apart from a few levels). The biggest change here though are the gold leaf tiles which produce extra sun. Somewhere in this world you'll get to unlock as a plant option too.

Here is a list of the unlocked plants in this world:

Red Stinger - Level 1
A long range plant which is stronger when planted close to home.

A.K.E.E. - Level 7
This plant throws small missiles up into the air that bounce from from zombie to zombie.

Endurian - Level 11
Like a wall-but but actually does damage to zombies that walk into it.

Stallia - Level 20
Slows down close-by zombies with a puff of perfume. Free to use but only lasts one hit.

Gold Leaf - Level 27
Turn ordinary tiles into gold tiles which help in sun production. Plants can be placed on the gold tiles.