Archaeologists have begun to excavate a mosaic beneath a corridor at Chedworth Roman Villa in Gloucestershire.
At 35m (115ft) long, it is considered to be one of the longest in-situ corridor mosaics in the country.
Visitors to the villa near Cirencester are able to watch archaeologists at work from suspended walkways which have been installed overlooking the mosaics.
National Trust archaeologist Martin Papworth said: "Hopefully we'll find some exciting things."
Victorian archaeologists uncovered and then reburied the mosaics about 150 years ago.