Southdowns Planetarium is a small, specialist attraction that adds a science stop to Chichester's cathedral-and-Roman mix. Its full-dome shows cover astronomy and space topics, usually with the intimate feel of a place run by enthusiasts rather than a big institutional museum.
Check the programme before going, because the planetarium is show-led rather than a drop-in gallery. When timing works, it is a useful family-friendly option and a good rainy-day counterweight to walking the walls or heading out to the harbour.