Chilterns walks: N-S Footpaths, churches, village wanderings and other places of interest PENN WOOD Nature puts on a fireworks display PINKNEYS GREEN Big skies offer room to breathe RUISLIP LIDO Beach that became a Londoners’ playground SHARPENHOE Clappers command an impressive outlook SHILLINGTON How fossil secrets sparked a mining boom SPADE OAK QUARRY Lakeside path comes into bloom