I love train sets, but we don't use ours nearly as much as we could — mostly due to the hassle of setting it up and the inability to leave it up (lest someone trip and fall.) This solution is the perfect answer to the sprawling train set dilemma!
Carla from small + friendly encountered the same problem — having enough space and storage to make train time a regular activity! She came up with this clever trundle table solution — a slide-out train table with a felt landscape, all ready to play with and so easy to put away.
Read more on Carla's blog, small + friendly.
(Image: small + friendly)

Nomade Express Slee...
Love this. Unfortunately our under-bed space is already used for toy storage, but this is awesome.
Here's another great DIY trainboard
http://www.younghouselove.com/2012/09/all-abord-the-train-board/
Think beyond trains. I would have LOVED a board like this for my toy farm & all its horses--by far my favorite toys--when I was a kid.
A friend used such a trundle for her kids' LEGO creations. 'Cause sometimes you build things that take more than one playtime.
Cute but I'm just not seeing the allure of a train table... so far at our house, the fun of a train set is actually in the taking it apart and rebuilding it at each playtime. That's what keeps my toddler busy and it seems to me that's the big educational piece to it too, because it's like a new puzzle every time. Plus, no table means no space limit - it's a blast building all the way around the dining table, etc. Occasionally we let a big project sit out for a day or two, just like with blocks, but only for as long as it's fun and not a hassle.