The Portal Master allows you to open portals on the World Map. Upgrading this building increases the duration of your portals. You can build the Portal Master on any large tile within your City as soon as your Capitol reaches level 10.

Click on any large tile you wish to place the building on.

Next, scroll sideways through the list of available buildings until you find the Portal Master icon.

You can demolish this building by following the instructions in this article.