To sit down and decide to perform a body of work 48-pieces strong is more than a mere undertaking — it’s a musical death sentence. Such time and devotion are rarely found in even the most dogged of performers, and it’s even less likely when the pieces themselves demand virtuosic gall from their challenger. But Craig Nies did exactly that, and five years later, he has succeeded. On Friday, the piano professor at Blair School of Music will finish his goal of performing all 48 preludes and fugues in Bach’s Well-Tempered Clavier. Since the spring of 2007, Nies has performed concerts combining these pieces with other notable composers’ works, ranging from Liszt to Chopin. His final show will not only have Prelude and Fugue No. 24 in B minor, but also Beethoven’s Hammerkavier Sonata, one of the most technically demanding solo piano pieces to date. So swing by tonight to hear some free classical, and make sure to give Nies a pat on the back for finishing his proverbial hike on the musical Appalachian Trail.