Meet the man on the 100RSD note at one of Belgrade's best museums, where you can release your inner nerd with some wondrously sci-fi-ish interactive elements. Tesla's ashes are kept here in a glowing, golden orb: debate has been raging for years between the museum (and its secular supporters) and the Church as to whether the remains should be moved to Sveti Sava Temple.
You are not obliged to visit by tour, but the price includes it either way and you'll miss some of the experiment demonstrations on your own.