Open at any reasonable time during daylight hours.
No admission.
Wikipedia https://en.wikipedia.org/wiki/St_John's_Abbey,_Colchester
English Heritage website http://www.english-heritage.org.uk/visit/places/st-johns-abbey-gate/
Address 25 Saint Johns Green, Colchester CO2 7HE, United Kingdom
Coordinates 51°53'7.908" N 0°54'4.702" E