Heureka is one of the best science centres in Scandinavia — a large, well-designed space where most of the exhibits are hands-on and genuinely engaging for both children and adults. The permanent collection covers physics, mathematics, biology, and technology through interactive installations that avoid the patronising simplicity of many science museums. Temporary exhibitions rotate through several times a year and are often excellent.
The building also houses a planetarium, an outdoor science park open in summer, and a decent café. It is a 10-minute walk from Tikkurila railway station, making it very easy to reach from Helsinki on the suburban rail. Expect to spend 2-3 hours minimum, more if you have children.