The Monastery of Santa Clara-a-Velha is an abandoned 14th-century Gothic convent rescued from centuries of submersion by the Mondego River. Founded by Queen Isabel in 1330, it had been slowly sinking since the 17th century due to repeated flooding. A two-decade restoration project spectacularly brought these atmospheric ruins back to life. The modern interpretation center explains the complex history and restoration work. The partially flooded building creates a unique atmospheric experience where water reflects the Gothic walls. Queen Isabel was originally buried here before transfer to Santa Clara-a-Nova.