If you're visiting Yerevan in the summer you'll experience sweltering heat during the day. No matter how thirsty you get, resist the urge to drink from any of the public water fountains around Yerevan. You will see many locals crowded around drinking from them but they have built up an immunity to the pathogens in the water. The public drinking fountains are not drawing from the municipal water supply but are pumped in untreated from other sources, so don't think you can drink from them even if you have been able to tolerate the tap water because it is not the same. I'm not entirely clear why the drinking fountains aren't using the same tap water supply, but it is something to keep in mind since you are almost guaranteed to contract a giardia infection from them. Don't do it.
Saint Hripsime Church is nearby the Etchmiadzin Holy See and was built in 618 AD. Armenia was the first nation to convert to Christianity, predating even Rome, and has some of the oldest Christian churches in the world. This church is named for Saint Hripsime, who fled from the Roman Emperor Diocletian's court when he made unwelcome advances towards her only to be tortured and killed by King Tiridates III upon reaching Armenia.