If you're in Kampong Speu and interested in visiting museums, a great option would be the Kampong Speu Provincial Museum. It's located in the center of town and houses a collection of artifacts and exhibits on local history and culture.
If you're looking for similar type of places nearby, you might consider visiting the National Museum of Cambodia or the Tuol Sleng Genocide Museum in Phnom Penh, which are both about an hour and a half away from Kampong Speu by car.