To add this Public Calendar to your own calendar, 

ICAL:    https://calendar.google.com/calendar/ical/ggtkddhmeuj3sbvio0v4447jho%40group.calendar.google.com/public/basic.ics

HTML:  https://calendar.google.com/calendar/embed?src=ggtkddhmeuj3sbvio0v4447jho%40group.calendar.google.com&ctz=America/New_York