Triple bunk bed
Last Christmas, when we had 16 extra people in the house, including 10 grandchildren, someone suggested I should build a "triple bunk" for those occasions. I'd just finished two sets of twin bunks for two of my children's homes and orders for one more in a couple of years.
Since the triple would be a once or twice a year use, I just made it out of southern yellow pine joist lumber, ripping out parts to make them quarter- and rift-sawn.
One end has an integral ladder into the upper two bunks built into their footboard.
To get maximal headroom, the mattresses are IKEA foam mattresses over IKEA laminated and crowned bed slats.