Author: F J Beerling; Welsh Adaptation: Gareth E. Jones.

Uarda loves solving puzzles and wants to become an engineer. She and young cousin Rhys are excited to meet the famous stone lions of Britannia Bridge. Uarda wants to find out how Thomas Telford built the nearby suspension bridge over the Menai Strait and Rhys accidentally discovers why Robert Stephenson couldn't use the suspension bridge for his trains!

Awdur: F J Beerling; Addasiad Cymraeg: Gareth E. Jones.

Mae Uarda, sy'n dwlu ar ddatrys posau, am fod yn beiriannydd. Mae hi a'i chefnder Rhys wrth eu boddau pan wnânt gyfarfod â llewod carreg enwog Pont Britannia. Mae Uarda am wybod sut yr adeiladodd Thomas Telford bont grog Menai gerllaw, ac mae Rhys yn darganfod, trwy ddamwain, pam na fedrodd Robert Stephenson ddefnyddio'r bont grog ar gyfer ei drenau!