Nearest station is arlesey
its a 6 mile ride, the first bit is quite flat, then its the last part to the sands thats uphill a bit which is the way you want it as the down is on the way home when you are tired
the ride usually takes about 25 mins to half an hour when ive done it
theres also a one stop shop and a petrol garage you pass, so you can get food / drink then and if your bike did get very muddy and you were worried about not getting let on the train, the garage has a jetwash
also has the air pump thing for your tyres if needed (my friend somehow got himself a puncture while waiting at stevenage station so was useful then
)