The circuit of Valletta's bastions can be walked end-to-end in about an hour, taking in the full perimeter of the city's 16th-century fortifications. The walk offers a continuous sequence of views — the Grand Harbour to the south, Marsamxett to the north — and passes several key points including the Upper and Lower Barrakka Gardens, the Sacra Infermeria wall, and the Hastings Gardens viewpoint at the far western tip. Most of the bastion walk is along paths directly on or behind the walls, which are massive by any standard — in places 20 metres thick.
The limestone was quarried from the site as the fortifications were built, which is why Valletta sits in a slight depression relative to the surrounding land. The fortifications were designed by Francesco Laparelli, one of Michelangelo's assistants, and the engineering is as good as the design — Valletta was never taken by force. Walking the circuit is the best way to understand the city's shape and the thinking behind it.