I visited Khor Virap by car which is the best and easiest way. In the morning I had been to Garni and Geghard and in the afternoon it was time for Khor Virap. Khor Virap is a couple of km off the road to the village/town Ararat. You could take a bus heading for Ararat and be dropped by the road. Then you will have a long and hot walk (no shadows around) to the monastery. If you go by public transport, make sure that there are busses going back to Yerevan.
In front of Khor Virap visitors can buy pigeons. Someone told me they are sacrificed, someone told me they were let to fly at an outdoor altar.
Anyway, at Khor Virap there is a place were animals (for ex sheep) are sacrificed.
It is believed that these old pagan rites were accepted because Armenia became a Christian country very early and by keeping some old traditions it was easier to get people to convert to the new religion.
The monastery is from the 12th century. According to the legend this is where king Trdates III kept St Gregory the Illuminator imprisoned in a well for 12 years because he was practicing Christianity. Trdates III later released Gregory and Armenia became the first Christian state in 301.
The Hyur travel agency offers trips to Khor Virap in combo with Noravank Monastery. It is a full day excursion but at least two hours are waited for lunch. It includes also a visit to the home-museum of famous Armenian poet who had the nerve to talk about the genocide of the Armenians in Turkey during the Soviet times when it was not politically correct to do so. The official line was that he had a car accident but the unofficial one was that KGB helped him to have it. Now the question is whether the unofficial line has not become official one and hence not very truthful.
The museum is interesting with its wall fresco of the poet whose, name I cannot remember, and many others whom he had to deal with during his tenure on Earth.