Although Harwich is accessible by road from the London M25 via the A12/A120, the best way to arrive is by rail, not least because Harwich International has its own train station, right next to the ferry terminal (Parkeston Quay).
HS1 Highspeed train to London St Pancras takes less than 20minutes from Ebbsfleet International, or 5minutes from Stratford International; glimpses of the London skyline can be seen from the windows on the left side of the train as you hurtle towards the city at 125mph. From St Pancras it is a 15minute underground ride to Liverpool Street Station (its quicker doing this than using the underground direct from Stratford International). A train then takes you to Harwich, although there is a very annoying change at Manning Tree; a small rural station with a coffee shop open at certain times. The wait there is around 30minutes.
Upon arrival at Parkeston Quay there is a short walk upstairs to the ferry terminal which is large and spacious with plenty of seating, large windows overlooking the port and some catering outlets. It is necessary to check-in before proceeding through to passport control and then onto the ship via a long covered walkway. Boarding commences several hours before departure therefore, I would suggest getting there a little earlier.
