Alexander Magyarics wrote about it:

“I've been playing with this idea for a long time – to create a packing puzzle where one of the pieces cannot be taken out of the box and it works as a moving obstacle to make your solving process more difficult. Three pieces must be placed in the 3x3x3 cube under the 'timber', you don't need to fill the opening completely. One unit cube of the 'timber' enters the inner 3x3x3 space – it ends its journey in the middle of the upper side (the same position as in the distribution pack). You can find several solutions to put the pieces inside but only one leads to the correct position of the timber. Disassembly level 7.6.8. The craftsmanship of Pelikan team is just stunning, I love the contrasting wood selection. I'm throwing a coin to wish you a good puzzling time!”

Fit the pieces in the box