The Roman Well in uphill Lincoln is finally viewable, after spending the last six months covered by condensation.
The problems began after a £1.18million restoration to the Bailgate, which included £180,000 on St Paul in the Bail.
Lincolnshire County Council had the remain cleaned, and had glass placed over it as well as railings and subtle lighting.
The restoration had caused the county council to overspend by 17%, but people were unable to see the well.
The problem has since been fixed with a £6,000 humidity system.
Senior Project Leader Les Outram said: “The Roman Well is a fascinating piece of Lincolnshire history, dating back to 1st century AD.
“A lot of work went into exposing and cleaning the original stone structure so we are really pleased to have successfully found a solution which enables everyone to clearly view it.
“A special humidity control system, which can be variably set for changing conditions, has been put in place which works by drying the damp air and directing this through ducting onto the underside of the glass viewing panel.
“This has two effects: it both takes out some of the moisture in the air and slightly warms the glass surface. The condensation forms when moisture in the air hits a cold surface and comes out of suspension.
“The damp air is then exhausted to the atmosphere above the suspended floor.
“We therefore encourage all shoppers and residents to visit the restored Bailgate and take in yet another piece of our proud history.”
A visitor information board will soon be going up alongside the Roman Well.