This cache is one of a series along Holywood Road in east Belfast - this one is located toward the upper end near Tillysburn. It's just outside the recently revamped Danny Blanchflower Stadium, named after the Northern Irish footballer who played for Tottenham Hotspur in the 1950s and 60s.
The cache is magnetic and just behind a lovely old ornate electricity junction box (which I think is now disused) - they don't make them like that any more! It is not, however, on the box itself.