I can reveal that even Steve hadn’t realised that it was that long ago.
The first Gn15 layout has to be Carl’s Squarefoot Estate Railway:

Of course, there's more here:
http://carendt.us/squarefoot/
Here’s Carl’s take on that time:
"It was early 2001 when Steve Bennett and I were corresponding about a descriptor for his newly introduced scale, and someone suggested Gn15 -- an American-style term to stand for a variety of proportions and gauges that might constitute the family of Large Scale model railways built on very narrow gauge rails -- a brand new idea at the time. The suggestion was accepted and took off immediately, boosted perhaps by the convenient consonant-pair, "gn," which lends itself to numerous puns and anagrams based on the silent "g" (and spurred forward by the splendid Flanders & Swan song, "I'm a G-nu"!).
Meantime I had constructed a crude locomotive and was building an experimental layout in "1:22.5 on 16.5mm gauge." The goal was to produce the smallest possible full, working Large Scale model railway. By mid-2001, it became the Squarefoot Estate Railway (photo attached and see <http://carendt.us/squarefoot/>) using Bennett's first historic loco casting, the Gnat. Steve was extremely busy filling orders for this fledgling scale, so the SFER actually turned out to be the first layout built in Gn15. In fact, Steve Bennett and his partner, Steve Warrington, for a time used the SFER as an advertising illustration in their handbills!
[Note: I have a scan of one if Steve doesn't!]
The "Squarefoot" also became the setting for a new website about very small layouts <http://carendt.us>. The rest is (somewhat chaotic) history."
Carl sent the above background to me on February 11th just a couple of weeks prior to his retirement announcement.
I was hoping that Carl might well contribute to this celebration however that now seems unlikely.
The suggestion I make, which can be discussed in this thread, is that a thread in Modelling Matters is started entitled Gn15 – 10th Anniversary.
The posts to show a single photo of Gnatterboxer's Gn15 layouts. In a sense it’s a duplication of the Virtual Exhibition but entries are not controlled by myself.
The first entry has to be the Squarefoot Estate Railway.
Others, no doubt, will have other ideas – over to you.
Finally here's the first Advert for Gn15 hardware:
