Do we have any surviving remnants or written accounts of pre-Roman buildings in Northern Europe?
There were many hillforts in Northern Europe built by the Celtics, some of which remain today, such as Solsbury Hill. Numerous Viking ring fortresses also exist, including Aggersborg.
Of course, there is also Stonehenge in Salisbury, and in Ireland Newgrange and the fortress Dun Aonghasa. Hope this helps.