Complex sentence: Hence, locks, narrow bridges, and junctions are the main sites, especially those where there is somewhere comfortable to sit or lean, with a good view of the water, and preferably where refreshments are available.
Split into simpler sentences: Hence, locks, narrow bridges, and junctions, are the main sites. It is even better if there is somewhere comfortable to sit or lean, with a good view of the water, and where refreshments are available.