Ingleby's a long way from the Peak District.

It is in Derbyshire - just a long way south of the "Peak District".  Ingleby Foremark is south of Derby city and close to the Leicestershire border.

Don't know why Northumbria is mentioned though.

I guess the Northumbria connection is because the supposed inmate was believed to have been a deposed king of Northumbria. 

When I saw the item at first I thought it was in the Magnesian around Cresswell/Worksop. I must admit having to look up Ingleby. Obviously the "by" indicates naming by Scandinavians.

I think describing it as a cave is slightly misleading as it's not natural - like the stuff under Nottingham and at other points along the Trent valley, it's been cut into the soft sandstone.

Yes, cut in to sandstone in a cliff face near the river Trent. I visited it a few years ago. Needs a bit of fixing up and a coat of paint. It is only a couple of miles from Repton, which used to be a big royal site for the kingdom of Mercia. Possibly the former Northumbrian king was exiled there so the Mercians could keep an eye on him? Quite a common thing throughout history for a deposed king that it wouldn't be politic to kill to be exiled to another country and kept under observation. Some decades later the whole area got invaded by Vikings who sailed up the Trent from the Humber estuary and spent the winter at Repton, which was the end for most of the Mercian royal family. Location is https://www.streetmap.co.uk/map?x=433929&y=327200&z=120.

The evidence base for the life of Eardwulf is a bit thin, and contradictory in places.

The original research has been published by UBSS, but there is a twelve month delay in making it available online. Has anyone seen the original article?