Marlborough is a delightful little town although it’s become overun with poncy coffee shops.
It’s chalk downland so obviously in the wet it’s bloomin’ awful. When it’s dry there’s some gorgeous scenery to be enjoyed. Would strongly suggest that you get hold of an OS Explorer map for the area.
In the meantime here’s a few suggestions:
North of Marlborough: Avebury/Fyfield Down/Barbary Castle/Smeathe’s Ridge. Further north (Swindon) is singletrack at Croft Trail.
South of Marlborough: West Woods/the enigmatic Wansdyke/Golden Ball Hill/Huish Hill/Oare Hill/Martinsell Hill and fort/Knaphill/Pewsey Vale.
East of Marlborough: Savernake Forest.
The Ridgeway is useful for linking, as is the Kennet & Avon canal, as is the Wansdyke.
That’s just a quick taster, you’re welcome to post up with any questions. I’m still learning new routes!