Hi there !!! I'm the author and I'm the one who commissioned Robert (I also did the original map). I'd like to mention the great work of Robert here. He's currently doing all the maps for Avalanche. Well worth it.

As for Caennyas, yes, there is, more or less, one single road from the "lower city" to the "higher one". Here's a description of the city, as written in Avalanche, I hope this answers your questions :
Presentation
Caennyas is the historic human capital on the lands of exile. Nowadays, it whiles its time away peacefully, far removed from the tensions gripping Carcandas and Raijuvak, the two main centres of power in the region. Caennyas was built along the shores of the Thelor, high up on a plateau where the river cascades into waterfalls. The river’s flow divides the city, separating the high city from the lower one. In that respect, Caennyas embodies something of the spirit of the lands of exile and its inhabitants. Like two solitary existences standing side by side in mutual ignorance. For centuries, all the way up to the hinterlands, the people of the lands of exile would look to Caennyas for protection. But things have changed since the arrival of the refugees from Saloy.

Population and power structure
The city is governed by a council of wise men headed by the regent Colbert. The council tends to the affairs of the city and does not interfere in the issues involving the kingdom at large. The order of Theobald is represented on the council and the guild of thieves holds no sway over its decisions. As a rule, corruption is virtually absent from the high city. The cult of Thikrum has set up a rear base in the city, but its presence remains extremely discreet. The army of Caennyas enforces order in the high city without abusing its authority. Much as in Carcandas, the population of Caennyas is diverse: humans, half-orcs, dwarves, half-elves… Its inhabitants have mastered a high level of art and craftsmanship and as a result, the cultural life in Caennyas is extremely dynamic.

Common Knowledge
Caennyas is cut in two: the high city standing above the mouth of the waterfall and the lower city lying below. The high part is the historic old city, which predates the arrival and settling of the refugees from Saloy who built its lower counterpart. Most of the city’s administration is located in the high city: the seat of council, the temple of Theobald, the main defensive positions… Peace is maintained in the lower city by the fourth division of the army of Carcandas which is stationed there. The atmosphere in the lower city is reminiscent of the winter capital, though the guild’s activity and influence are maybe less overt.

Statistics and miscellaneous information
Caennyas’ tranquility is only broken on the rare occasions when white orcish incursions reach its walls during the winter. In such cases, the whole of Caennyas relies on the high city’s troops for protection. The seasonal migrations of the refugees from Raijuvak mean that Caennyas is particularly bustling in spring and autumn. On the outskirts of the lower city, part of the civilian population evacuated from Raijuvak lives in a temporary camp. Though it is located nearer the lower city, the camp and its refugee population are under the protection and authority of the high city’s council. As a result, the knights of Theobald and the soldiers of Caennyas can be found there, tending to the population’s needs. Numerous merchant convoys journey between Caennyas and Raijuvak.