The church services are held in Saint Basil's Cathedral nowadays.

Summary: The text states that Saint Basil's Cathedral is open to the public as a museum. It does not mention whether church services are still held there.

Detailed analysis: The provided text focuses on the history and current status of Saint Basil's Cathedral as a museum and a World Heritage Site. There is no information given about ongoing church services.

Conclusion: Based on the text, we cannot confirm if church services are held in Saint Basil's Cathedral nowadays.