A good way to trace through the history of Armenia, the Armenia Heritage Trail is a suggested itinerary of places which try to chronologically take you through the long and rich history of Armenia.
Erebuni - Urartian fortress which established the city of Yerevan in 782 B.C.
Cave in Khosrov - (optional) cave deep in Khosrov Forest State Preserve with pre-Christian inhabitation.
Garni Temple - First century Roman temple in Garni village.
Khor Virap - Monastery at the foot of biblical Mt. Ararat, where St. Gregory the Illuminator was imprisoned in a deep pit until he converted the Armenian King and thus nation to the first Christian country in the world.
Dvin - ruined capital of Armenia.
Echmiadzin (3 main churches) - Seat of the Catholicos (Patriarch) of the Armenian Church.
Oshakan - church where Mesrop Mashtots, inventor of the Armenian Alphabet in 405 AD is buried.
Ashtarak churches - the town of Ashtarak has some very old churches, including Karmravor, Marianne, one more rebuilt church, two in ruins and an old bridge.
Hovhannavank/Saghmosavank - two very fine monasteries perches on the edge of the cliffs of the Kasagh gorge, within distant view of one another.
Kasagh Basilica - ancient black basilica in the town of Aparan.
Odzun - an advanced seventh century basilica in the village of Odzun.
Haghpat/Sanahin - two extensive UNESCO World Heritage Site monasteries in villages overlooking the Debed canyon.
Kobayr/Akhtala - two beautiful monasteries with great frescoes showing a heavy Georgian influence due to the intertwined rulers at the time.
Mikoyan Museum - A museum honoring to brothers born in the village of Sanahin, one of whom invented the MiG fighter jet and the other served as Chairman of the Presidium of the Supreme Soviet in the 1960s.
Ijevan - Small museum dedicated to the coming of Soviet rule to Armenia. Also has nice traditional town architecture.
Dilijan (lay architecture - pre-soviet and soviet) - nice traditional town architecture.
Dilijan (Sanatoriums, cinematographers house, other Soviet architecture) - also home to many huge Soviet sanatoriums, some are pretty cool 70s (cinematographers house), some massive classical (Lernayin Hayastan resthouse?)
Republic Square/Yerevan Opera House - Yerevan was the focus of the Soviet building effort in Armenia, and Republic Square is a massive square with huge buidings full of columns, carvings and nice stone. The Operahouse, from the very early Soviet period predates the real Soviet style of architecture.
S. Grigor Luysavorich Cathedral - massive post Soviet cathedral.
Northern Avenue - large pedestrian avenue linking Republic Square to the Opera area which demolished all the old buildings in its path.
Other options off the route
The following sites are off the route, or out of order for this route, but I have listed them as they help fill in for periods which are not as well represented as others.
Metsamor - ancient settlement (previous capital), nice museum