If you are arriving at terminal 1, 2 or 3 leave the airport by following signs to M4 Central London. When you get to the M4 turn left following signs to "The West". Stay in left hand lane and turn off onto M25 sign posted Watford, M1 and M40.
If you are arriving at terminal 4 follow signs to M25, then go right onto M25 following signs to Watford, M1 and M40.
Stay on M25 until you get to junction 23 (South Mimms services) and turn off onto A1(M) going North towards Hatfield and Stevenage. When you get to Junction 9 (sign posted Baldock) turn right onto the A505. Carry on along the A505 until you get to a large roundabout with the A10. Turn left onto the A10 (sign posted Cambridge) and then take the second turning on the right (sign posted Melbourn, Meldreth and Whaddon). Riverside Guest House is the first building you come to on the left hand side, opposite the Sheene Mill restaurant.