Valletta is tiny — about 800 metres by 600 metres — and entirely walkable. The main grid of streets is flat at the Republic Street level but drops steeply toward both harbours via a series of stepped alleyways and cross-streets. From City Gate to Fort St Elmo is a 20-minute walk. You can cover the entire city on foot in a morning without rushing.
There are no taxis within the city walls and no practical need for them — everywhere is within walking distance. The main challenge is the hills: the cross-streets running north to south can be steep, and the descent to the waterfront from the bastions involves stairs. The waterfront areas — Grand Harbour to the south, Marsamxett to the north — are accessible by lift from the bastions in a couple of places, or by walking down the ramps near City Gate.
The ferry to Sliema departs from the Valletta waterfront below Hastings Gardens, running a continuous service throughout the day. The ferry to the Three Cities departs from the Grand Harbour waterfront below the Lower Barrakka Gardens.