The Roof Garden at the Trafalgar Hotel in London's West End. You can't really find a venue more central than this and the views are so appealing, not the highest (six stories), but there's much to watch below.  The Traflagar Hotel is located in the corner of Trafalgar Square, near Admiralty Arch.

The Roof Garden is only open for part of the year, since London's climate is not conducive to year-round al fresco refreshment, it's best seen during the summer months, when the square below is heaving with oblivious tourist crowds. Be sure to ring ahead before a visit, as private parties may mean the bar is temporarily closed to the public.

The Trafalgar Hotel to which the Roof Garden is attached, is part of the Hilton stable and is their first stab at a boutique hotel. It has minimalist, cool interiors and couldn't be better placed as far as visitors are concerned. Major galleries are on the doorstep, Buckingham Palace and Westminster are 10 minutes leisurely walk away and Leicester Square, Piccadilly Cicus and Covent Garden radiate out from Traflagar Square. Handily placed for theatres, the Royal Opera House and ENO, which is just across the square.