Okay I'll start at the beginning.
Flew SYD-SIN-MXP. We had a couple of small day packs, a large wheeled bag and a small backpack which could easily pass as cabin baggage and I usually take it on board.
However, as it happened we checked both our bags right through to Milan (with an overnight stopover in SIN) to save the hassle of carrying for that night.
On arrival in Milan (Malpensa, which is a looong way from Milan) we got to the baggage carousel and spotted our large case, grabbing it with glee due to its prompt arrival and headed out into the terminal.
We sat down to look up info for the bus transfer to Milan and set up my e-SIM then I went to look for something in the second bag... when I realised I'd forgotten to collect it. Okay I'll just walk back through... er, no... (too much domestic travel)...okay now what?
Luckily I stopped a woman in airport uniform and told her my predicament. She told me to head up past [something I didn't understand] to Lost and Found.
After some searching I found the entrance where I had to go through security and the staff member at the desk said something like "you look lost, my friend, what are you requiring?" so I told them and they pointed me back into the carousel area which was along a very weird long corridor with a few mysterious doors and occasional travellators along it (I was expecting to be challenged at any moment) until I arrived back at the carousel and there was my bag! Headed back outside to start my adventure.
No harm done.