Murble's unique navigational skills have earned him a special prize - his travel plans will be decided for him by the organisers, who will instruct him on exactly which tickets to buy, lest he accidentally try to route himself via Iceland or - even worse - Glasgow.
Alfriston is most easily reached along a lane that turns south from the A27 road between Polegate and Lewes. Here's a map. If driving from London or anywhere north or west of there, head for Brighton and then go east on the A27. If arriving at Dover or Folkestone, follow signs to Ashford, then Rye, Hastings, Eastbourne, and then follow the A27.
Ferries run between Newhaven and Dieppe and Le Havre. From Newhaven harbour, either take a train to Lewes and then to Berwick, or drive to Alfriston via Seaford. See the map link above. Those who are feeling particularly adventurous might like to row from France to the beach at Coombe Haven and then walk five miles up the valley.
There are also ferries between Dover and Calais/Dunkerque. Rowing across that particular part of the Channel is not recommended, due to drunken Elbonian tanker captains.
The nearest station is Berwick (that's Berwick, Sussex, not Berwick-on-Tweed), two miles north of Alfriston. There is a local bus, although we don't yet know how often it runs - but if the bus isn't convenient, we will arrange something. There are direct trains from London Victoria, Gatwick Airport, Brighton, and Ashford International, although in all cases it's better to get the first train to either Berwick, Brighton or Lewes (or Eastbourne if coming from the east) and change if necessary.
The nearest major airport is Gatwick. From there you can either hire a car, or catch a train.
Bus services are somewhat chaotic and infrequent :-) The local Cuckmere Community Bus service, run by volunteers, has a small fleet of minibuses. We expect to hire one or two of these for trips and also maybe to get people to the start of walks without the usual hassle of finding enough cars.