There’s nothing like hiking across moors and encountering castle ruins to ignite the creative process—as Mendelssohn experienced it on a tour of Scotland. Holyrood Castle (where Mary Queen of Scots was crowned) inspired the mysterious mood of the Third Symphony’s opening. But the mists ultimately lift in the sunny, lively finale. Plus, Portland favorite Conrad Tao dazzles in Mozart’s 21st Piano Concerto, with its slow movement once described by biographer Maynard Solomon as “an entire movement of unrelieved, time-stopping beauty . . . for something just short of eternity.”