The region of Artsakh, Nagorno-Karabakh is a self-proclaimed republic, not recognised by the United Nations. It has been autonomous, aligned with Armenia, since the mid-90s. It has a majority population of Armenians, yet the territory, under international law, falls within Azerbaijan.
There are no flights to the area; access is by road from Armenia through the Lachin Corridor. For independent travellers from Yerevan there is a bus service, 'Marshrutka' minivan taxis and tour group people carriers. Visitors to the area risk being denied entry in the future to Azerbaijan.
Both Spain and the UK have travel warnings in place with regards to the region, since the disputed territory has an active line of contact with Azerbaijan. Armenia and Azerbaijan are said to be engaged in ongoing peace talks.
(This feature is not intended to recommend travel to Nagorno-Karabakh, it is simply a personal perspective, without any endorsement by the author or the publisher of Nagorno-Karabakh or any of the relative geopolitical issues.)