So far, the areas go:

Keystone: The starting town. There are various buildings here.

Location |              Place              

Top Right    | Youll find the armory up here.

Btm Left      | Down here, you will find the inn/ item shop.

Above Start | This is the town hall. You can buy houses, bank your coins, or buy some magic in here.

The Path to Mushroom Kingdom: The path to the legendary Mushroom Kingdom (not made yet), it holds various foes. It is divided into two parts, the above ground and the below ground. The latest addition would be the bean bean path. It is a warp pipe after the cave.

Location: North of Keystone

The Infernal Desert: Money and traps are hidden in this desert, reached via a warp pipe in the cave.

Location: The path to Mushroom Kingdom cave

Mushroom Kingdom: New spells, new houses, new areas, new monsters. The first of many areas, this one resembles a town from Mario and Luigi: Superstar Saga.

Location: Warp pipe via Cave

The arena: The hotspot for PvP. With a saving scoreboard, the top battler (or spectator..) will always be known!

Location: Top-Left of Keystone

And, who can forget the best area. The Player Built Area! Here, players meet and build together. Here is a sample of what is built.

Location:  Bottom-Right of Keystone