The Royal burial church is open for self guided tours, weekends until November. Combination ticket including a visit to the Royal palace is available.
The Riddarholmen Church is the final resting place of the Swedish kings and Stockholm's only preserved medieval abbey. It is also the church of the Order of the Seraphim, with the coats of arms of deceased Seraphim Knights.
You can explore the Riddarholmen Church by yourself. Signs and guide book are available.