If you ride up the main climb on Portland (having ridden the Rodwell trail and then the causeway) there used to be some interesting riding above Westcliff overlooking Lyme Bay around the quarries. It’s more old skool XC really, as is most of the riding around the town, but spectacular views.
Have a look on an OS map at the amount of bridleways that exist around the town – especially along the Ridgeway (between Weymouth & Dorchester). I’ve not ridden there for years, but for a good old fashioned XC ride, going west along the Ridgeway brings you to Hardye’s Monument, and east takes you around Came Woods and across the top of the White Horse. There are bridleways that drop you off that south to Sutton Poyntz and Osmington – it’s mainly tracks but really lovely scenery.
Puddletown Forest used to be great fun too, back in the day (early ’90s… ahem!)
Have fun 🙂