What I'm talking about is the LEGO Billund Airport (4000016). Never heard of it? Either had I until earlier this week.
Basically, it's super-duper rare, with only 10,000 sets ever produced. Want it? You'd have to be flying through Billund Airport (one of Denmark's busiest air cargo centres). The airport also services some regular commercial airlines, and it's the airport you want to be flying in and out of if you're visiting Legoland - given it's just around the corner.
The set was designed by Billund Aiport employee Lennart Cort, who works in the airports LEGO store. He created the set, and after showing it to his manager it was then shown to the LEGO Group management, and it was soon made into a set.
I haven't read much more about the set, but it appears to fall into the LEGO Architecture category (given the box art and style of build). Compared to the other LEGO Architecture sets, it's a little abstract. Billund Airport is a big structure to be able to replicate on such a small scale, yet still get all the detail.
By the looks of things, the set actually consists of two separate models (so-to-speak). The little yellow bus is a nice touch, and the styling of the main building really captures the appearance of airports' drop-off and pick-up canopies. The aeroplanes are very cool - five small, two large - which fit in well next to the aerobridges.
Anyway, I'm presuming that you haven't been to Billund Airport recently and/or don't plan on going there anytime soon. If you want the set that much, there are some really cheeky buggers selling their sets on eBay for a very exorborant price (I do NOT condone this re-selling). But heck, for $600, you might as well take a European holiday, and pick yourself up a set on the way to Legoland.