For history & culture, Powder Tower (Prašná brána) is hit or miss.
A handsome, central medieval landmark and a cheap climb for a mid-level Old Town view. The catch: it's genuinely minor — a steep stair to a modest panorama lower than the bridge or Petřín towers, and the exhibition inside is thin. Best appreciated from outside as you pass; climb only if you're a completist or it's raining.