Planning solo days when most attractions are more fun with company

Some attractions feel designed for groups: guided activities where everyone arrives with friends, themed restaurants with big tables, long scenic drives where no one shares the navigation. I'm happy alone most of the time, but a whole day of those can feel odd. I've started mixing a social activity with several things I naturally enjoy solo, like museums or long walks. How do you plan days that feel complete without turning every trip into a search for companions?