VII. Nehellenia
Venerated at two shrines on the North Sea (in modern-day Netherlands), this Goddess is likely a non-Celtic deity who was introduced to the Celts when they arrived. Her name means nothing in Celtic, but appears to mean something like "Steerswoman".
Her iconography is interesting:
Her on a ship's prow
Shown with dolphins
Always with a dog (unusual for a female Celtic deity)
Her shrines have her in "cave-looking" places, under cannopies, etc.
Interestingly, both her shrines were taken by the North Sea, which engulfed them during antiquity.
Her cult was very rich, and consisted mainly of maritime traders and merchants.