McCaig's Tower is Oban's most distinctive landmark, a granite colosseum perched on Battery Hill above the town that is visible from the water for miles around. The resemblance to Rome's Colosseum is deliberate — McCaig admired classical architecture and hired Edinburgh stonemasons to execute his vision — though the scale is much smaller.
The tower was never completed, so its interior is a walled garden, open to visitors without charge. The walk up from the town centre takes about ten minutes and the views from the surrounding path are excellent — across the bay to the island of Kerrera, beyond to Mull, and on clear days further still. Go early in the morning or in the evening for the best light and fewer visitors. Atlas Obscura notes it as a place that looks like a Roman ruin that arrived in Scotland by accident, which is not far wrong.