Rakvere Castle (Linnus) sits on Vallimägi, a stubby hill at the south end of the old town. The medieval walls are largely gone — what's there now is a partial reconstruction filled with a hands-on living-history attraction aimed (cheerfully) at children. Knights, archers and craftsmen demonstrate medieval life, you can fire a crossbow and beat on a forge, and the basement contains a properly grim torture chamber.
It's better than it has any right to be. The kids' aspects don't overwhelm the place — the views over Rakvere from the ramparts are genuinely good, the cellar exhibits explain the Livonian-war background in plain English, and on a sunny day the whole hill becomes a picnic spot. Open daily from late spring to autumn; reduced hours in winter.