Bukit Tengkorak is Semporna's best land-based sight, a volcanic hill where archaeologists found evidence of prehistoric pottery-making and trade links across the Celebes Sea. The small museum gives the context; the short path up the hill gives the view.
Come here if you have a spare hour before a bus or flight. It will not compete with the islands, but it does add a bit of history to a town that otherwise feels built around boats and dive tanks.