Dilijan is a resort town with mild climate, fresh air in the northeast of Yerevan. It is famous for its amazing surroundings, called the "Armenian Switzerland" by the locals, due to the densely forested valleys and mountains with alpine meadows around. It is an excellent center for walking.
Most visitors to Armenia spend all of their nights in Yerevan. Spending a night or two in Dilijan while exploring Tavush Marz is well worth it. There are plentiful accommodations in Dilijan, from the luxury of the Tufenkian Hotel to much more basic hotels or homes. From Dilijan you can explore up to the Georgian border and the remote Shamshadin region much more easily than from Yerevan, and then continue on to Lori Marz.