To honor the release of “Plays Metallica by Four Cellos” 20 years ago, Finnish cello masters Apocalyptica have two concerts planned for Warsaw and Wrocław. Their popular debut album of Metallica covers will be re-released in July 2016 with three additional songs: “Battery,” “Nothing Else Matters” and “Seek & Destroy.” Combining metal and classical music while developing a devoted following for the last two decades, Apocalyptica’s eighth and latest album, “Shadowmaker,” was produced by Grammy winner Nick Raskulinecz, who has worked with the Foo Fighters and Mastodon. Critics noticed inspirations from Alter Bridge or Alice in Chains, but the album also boasts the strictly instrumental songs for which Apocalyptica is known.