The arrow indicates entrance track to site.
The site is the white area between the railway, river and footpath under the railway.
The Bidwell Centre is roughly under the "m" of Two Mile Bottom.

(Aerial view blatantly lifted from Google Maps)

The Bidwell Guide and Scout Centre is situated off the A134, two miles north of the A11 Thetford by-bass.
OS Land Ranger Sheet 144, Grid Reference 846 873.
Nominal post code for GPS navigation systems is IP24 1LZ. The access track does not generally appear on electronic maps.

Important note:

The railway bridge that goes over the access track to the site is very low - less than 8ft clearance. If you are intending to bring a vehicle on site that is taller, please be sure to ask about the alternative access route that doesn't have a height restriction when making your booking.

Access sign viewed approaching from the north along A134 -
conveniently there is a similar sign when approaching from
Thetford and the A11 in the south.

Make sure you take the left fork of the access
track as indicated by the Bidwell sign.
Or you'll end up in the woods.