In the past few years, we have covered plenty of awesome space saving products from Expand Furniture. These Hidden Vertical Murphy Bunk Beds are also interesting. They hide in a cabinet but can be lowered down and lock in place to accommodate two people. You also get a built-in ladder with these. Guard rails can be used on the upper bunk.
You get multiple finishes to choose from. This bunk bed system is made in Italy. Not cheap though.