Stavropoleos monastery, founded in 1724 by the Greek monk Ioanikie Stratonikeas, is a masterpiece of Brancovan architectural style and a little oasis of tranquility in the heart of the old town. It's also one of the oldest and most beautiful churches in Bucharest, due to the rich stone-carved decorations and frescoes painted on the walls.
Stavropoleos monastery is also one of the very few churches in the old town center which survived the Big Fire in 1847, that destroyed a large part of the old city. You should come here in summer and spend some time in the courtyard and you will instantly feel the peace and tranquility surrounding you.
Come here for the liturgy on Sunday mornings and take some time afterwards to admire the original church paintings from the 1720's.