A team of archaeologists have been conducting their third dig in recent years at National Trust venue Attingham Park, near Shrewsbury.
The work is the continuation of efforts from 2018 where the archaeological team discovered a long-lost summer house.
The latest dig, which started earlier this month and finishes on Friday, has been looking in the same area and has uncovered what is believed to be a 'plunge pool'.
According to Dr Nigel Baker, project archaeologist on the dig, the perfectly oval remains are thought to be the remnants of a private pool created for the Second Lord Berwick between 1810 and 1820.
Dr Baker said: "In 2018 the National Trust initially asked me to take some volunteers and do an excavation and check out where they wanted to put some new roads in, and to everyone's surprise we found the remains of a Georgian summer house that no-one knew was there.
"We had a second dig in 2019, and after last year was off because of Covid we are now back on the third, and what we think will be the final session, to look at bits of the summer house which we didn't understand, and its surroundings."
He revealed how they had made the latest find, saying: "We were asked to check out a slight depression in the field here. They didn't know what it was and basically a couple of hours' work with a JCB showed there was an oval brick pool there.
"We think it was a 'plunge pool'. We think that because they are often found in association with summer houses and gardens of stately homes and country parks.
"We can't prove it – it could have been an ornamental pool or a pond, but the chances are we think it was a private pool for the Second Lord Berwick, built between 1810 and 1820."
The area will be digitally surveyed on Friday before being covered back over to protect it from damage by frost or bad weather.