Grandpa's homebuilt trailer. After adjusting bearings and wheel alignment, I had used it for some time and got addicted very quickly. Unfortunately, it soon went back to the attic - grandpa had no regulations to follow, so the trailer is wider than today's road-legal maximum.
Frame is welded from bent round tubes, cargo deck is a wooden lid of some crate. Wheels are 26×1+3/8" (standard front ones from scrap bikes) with beadless "Pfalz" tyres (I hope I spelled it right). The drawbar has a socket on its end that can be hooked on some bolt or hook under the saddle. Disconnected trailer can be also pulled by hand, which is a handy feature.
The frame is designed for minimum possible length of tubing, you would need to use cantilevered wheel axles to reduce it any further. It has a drawback though: the drawbar, forks and wheels are quite flexible (big wheels are generally not a good choice for a multitrack trailer). Another drawback is the trailer is very big on all sides and parking it is difficult if you don't have a garage.