Complex sentence: There are very few traces of the mansion of Heanton Satchville surviving today, but it was at one time "one of the most imposing houses ever to exist in Devon", in 1674, it was the second largest house in Devon.
Split into simpler sentences: There are very few traces of the mansion of Heanton Satchville surviving today, but it was at one time "one of the most imposing houses ever to exist in Devon". In 1674, it was the second largest house in Devon.