And if you're going to Swinley this is a good overview resource: http://www.essexhertsmtb.co.uk/mtb-trails/swinley-forest.php
The closest mainline station to the office and the Hilton you're in is Waterloo, so it's pretty convenient though you'll need a cab from the station at the other end to get to Swinley Trail Centre itself to pick up the bike.
@Velocio started
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And if you're going to Swinley this is a good overview resource: http://www.essexhertsmtb.co.uk/mtb-trails/swinley-forest.php
The closest mainline station to the office and the Hilton you're in is Waterloo, so it's pretty convenient though you'll need a cab from the station at the other end to get to Swinley Trail Centre itself to pick up the bike.