A group of us did a figure of 8 circuit of Bull Island the Sunday before we all locked down in March 2020, also didn't occur to look for a high point. You can do a very nice c. 10k figure of 8 circuit of the island, starting at the causeway, following the outer beach towards Sutton until you're forced into the dunes, follow a trail back along the inner lagoon, skirting St Annes's golf club back past the causeway until you meet the Bull Wall. You can include the Bull Wall as part of this terribly arduous "trek" or else follow the outer beach back to where it meets the causeway roundabout. About 2.5 hours. One warning, if it's a nice weekend get there early as parking can be a nightmare. Also if it's windy be prepared for a lot of windblown sand when you're on the outer beach and watch for golf balls when going by St Anne's Linkback: https://mountainviews.ie/summit/2328/comment/23405/