Minecraft 1.5_1 Achievement - On A Rail (probably outdated)
1 BLOCK = 1 METER
"Travel by minecart at least 1 km from where you started. "
so anyway I pretty much build this entire railway thingy after I realised that weird achievement "on a rail" ain't gonna play off after my 15min attempt on a forever looping rollercoster (that was almost 6 km) (check my channel for vid of the coster thing).
single redstone torch markers every x50 rails, and
double redstone torch markers every x100 rails
the big squar-ish thing at the end indicates the 1000 blocks/rails checkpoint :)
cheers