Torksey Castle, an Elizabethan Manor House located on the east side of the River Trent (today it's in the River Trent)
It is a 16th-century Tudor stone-built fortified manor house founded by the Jermyn family of Suffolk. It is Grade-I listed and a scheduled ancient monument. In 1645, the property was slighted during the English Civil War. Having been taken from the Royalist Jermyn family by Parliamentarians, it was burned by Royalist soldiers based at Newark.
I reckon English Heritage should try and take it over, they like ruins.