The Lost Cities Mod

The Lost Cities mod allows you to have a completely new and unique survival experience. With this mod installed, you will be given an additional 'Lost Cities' world type in your world creation settings. A world generated with this worldtype setting will have plenty of buildings, highways, bridges, tunnels, dungeons, etc. So you will be having very large cities to explore the moment you spawn into the world. Furthermore, some of the buildings will have open or hidden loot chests in them. 

It is important to note that you have to set 'Lost Cities' as your world type while generating a new world, in order for this mod to work.

Take a look at the screenshots to see what you can expect from this mod. This is a Forge mod and download links are given below. Read the installation instructions CAREFULLY to avoid any errors.