A mildly steampunk laser cut version of Durovis OpenDive VR goggles.
This version is a bit more stable and less shaky than joo's, and does not require any 3d printed parts.
Originally designed for Nexus 4, tested with Nexus 5, should be compatible with all devices of similar size.
First, you'll need the Durovis lens and strap kit from amazon.de (http://www.amazon.de/dp/B00COO64IC). It costs 6.99 EUR and its worth every cent.
Laser cut the source file from 3mm MDF, with the red parts cut out first. Use M4 bolts to put it all together, and a bit of glue to hold the lenses to the frame. The "flatter" side of the lenses should face the eyes. Use rubber bands to hold the phone in place, and to keep the lens contraptions in place. Do not tie the bolts on the sides too tightly so you are able to adjust the lenses as needed.
The whole thing cost me about 12 EUR, and it is quite fun to play with.
Enjoy! Let me know if it works! :)