 To the east of the courtyard lies the Keep . It was re @-@ built in the 1830s , having previously lain in ruins . This area has the largest concentration of students living in the castle . To the south of the courtyard is the Gatehouse , built originally by Hugh de Puiset in the 12th century and re @-@ developed in the sixteenth and eighteenth centuries . Around this are the college 's more modern offices . 
