Sorry just seen this.
Unfortunately, the woods around Sheringham Park have been decimated by forestry to the point where most routes have gone, it was good there in that there was elevation and ups and downs, you can still ride the coastal path up the cliff and Sheringham.
There is riding to be had at Shouldham Warren and Santon Downham woods if you follow Strava routes from there, used a lot by Kings Lynn MTB for their race series.
Some fun to be had riding around the Wells/Holkham area in the trees behind the beach and on the coastal path which allows bikes on that stretch.
The bank holiday weekend has Pedal Norfolk festival at Holkham Hall where there is MTB racing so riding to see that could be combined with the above?