стены собора были отреставрированы,

стены собора были отреставрированы, с тем что бы они вновь обрели свой внешний вид

Результаты (английский) 1:

the walls of the cathedral were renovated, so that they have regained their appearance

Результаты (английский) 2:

the walls of the Cathedral have been restored so that they regained their appearance

Результаты (английский) 3:

the walls of the cathedral was renovated in order to recover its appearance