Assumption Cathedral, Sergiev Posad
This is my favourite of the many beautiful churches at the Lavra of Sergiev Posad east of Moscow. It dates from the mid-16th century and was also the church Ivan the Terrible liked best, from what I have read.
On my most recent trip to Russia we didn't have a lot of time to explore this amazing collection of churches and monasteries, considered the centre of Russian Orthodox Christianity until 1920 when it was closed by the Bolsheviks for a time. I was glad I had been there previously, and had a chance then to hear the monks chanting in another church.
I'm not sure but I suspect this is the church that featured in the film The Russia House, starring Sean Connery and Michelle Pfeiffer. In any case it is well worth a visit if you are looking for a relaxing day trip from Moscow.