Black Mountain sits in the Belfast Hills to the north-west of the city and offers the best vantage point you'll find without leaving Belfast. From the summit at 390 metres, the whole city spreads out below, the lough, the Harland & Wolff cranes, the hills of Antrim and Down beyond. On a clear morning it's one of those views that resets your sense of scale.
The main trailhead is off the Blacks Road and the walk to the summit takes around two hours return, depending on pace. The path is well-established but the terrain is open moorland, bring proper footwear and a waterproof layer regardless of the forecast. A flask of something warm makes it better.
Go on a weekday if you can, weekends bring more walkers. Sunrise walks are possible from late spring and the light over the city in the early morning is worth the early start.