The best place to start is Bucovina, in northern Moldova. There is no other place in the world with so many Orthodox monasteries and with such high quality exterior frescoes. These painted monasteries are so beautiful and so rare, that they have been added to the UNESCO World Heritage in 1993. The presence of these monasteries have transformed Bucovina in one of the most attractive and most visited touristic areas in Romania.
The Wooden Churches of Maramureș should be next on your list. They are considered to be unique, because of the way they combine Gothic style with traditional wood construction. They show a high level of craft skills, are narrow, tall and covered with shingles. Eight of the churches of this mountainous area of northern Romania have been included in UNESCO World Heritage in 1999.
These two areas of Romania have the highest concentration of monasteries, but they can also be found all over the country. And if you think that just a couple of hours visit is not enough, many of the monasteries will be more than happy to offer you accommodation.