A Broken Vanilla End Portal
A broken vanilla portal; Note that in a Vanilla installation the Portal Blocks in the middle would have remained intact.
An Opened Crafted End Portal
A Vanilla End Portal
For references.
A Closed Crafted End Portal
An Example Build
I thought my design looked kind of ugly at first but this made me change my mind (:
End Portal Frame Block
Note that you need 12 of them to make a complete portal.