The Moon Pass is an ancient, spectacular, sheer-sided gorge splitting the Nether Mountains into two ranges, towering on either side of the River Rauvin with an east-west bend in the middle.
The Rauvin is often called "The Road Through the Marches" and its icy waters are navigable from Sundabar to Silverymoon. The Moon Pass Gorge, however, is impassable without the help of a strong and experienced tow-team from the shore, equipped with multiple lines, or, even better, two teams operating from both banks. Without such assistance, vessels tipically either capsize or smash against the rocks.
Worn towpaths, resembling wide ledges (lacking railings or handholds) were long ago cut into the cliff walls by dwarves and gnomes, and flank both sides of the river, maintained only by usage by the towteams.
The towpaths are too narrow for wagons, and run unbroken along both sides of the gorge.
No wagon road crosses the Moon Pass, but two high, treacherous mulepaths clinging to the slopes of the gorge allow (difficult) passage through the mountains to travelers on foot.
In Lore of Luruar, passage throgh the Moon Pass, both by river and by foot, has been interrupted by a (not entirely natural) rock fall which formed an impassable dam, blocking the road and the water flow, except for the occasional waterfalls spraying among the rock fissures, projected by the pressure of the water-mass pushing against such gigantic stones. The gorge behind has been filled with the water of the blocked river, and the foothpaths have been submerged.
The foregoing is nothing more than a plot device. I have often wondered about the motivations driving a PC through a RPG and, specifically, the motivations inducing a PC to accept a quest. Any quest, even the main plot. Of course, doing quests is quintessential to a RPG, so it is in a way assumed that the player is interested and willing to undergo quests. However, considering the variety of character personality, background and other features allowed by a D&D based game, I have always been intrigued by the question "why should this particular character be enticed by and accept this quest?"
I don't want to go philosophycal, but I believe that most "chosen one" story-lines, albeit often ferociously criticised, simply intend to provide an answer to that question, in order to offer a plausible play-through motivation to any kind of PC, hence to the widest possible public of players. Side-quests are more complicated though, especially in their typical layout of "helping somebody with something". So, their acceptance is frequently driven by very simplistic motivations such as the PC's good nature / sense of duty / interest for reward.
In Lore of Luruar there is no "chosen one" path. The plot unfolds and the PC can stick to it for a number of motivations and personal beliefs/interests, pre-existing to the plot or stirred by the four companions, which I won't spoil. The PC's doings will ultimately result in saving the Silver Marches from great perils, but the PC is not at all required to have such goal. In fact, the existence of a threat to the confederation will not be revealed to the PC until late in the game (differently, the player will receive hints as to what is going on, a bit à-la-OC with the initial Black Garius cut scene).
Paradoxically, though, just the PCs who might indeed have the goal of saving Luruar, may be refrained from undergoing the adventure. This may be particlarly true for lawful PCs.
The fact is that, when beginning the mod, in the town of Jalanthar, the PC will be automatically assigned a quest, which is necessary to provide a bit of background and to justify the presence of the PC in Jalanthar itself. Specifically (no spoiler, as this will be said upon modul load), the PC has been informally asked by a friend, member of the Council of Elders of Everlund, to investigate upon the rumors of fiends reported in the Sundabar Vale. Such fiends should be escapees from Hellgate Keep, destroyed in a epic battle just a couple years before.
So, for those unfamiliar with the geography of the Silver Marches, the PC travelled from Everlund to Jalanthar on the road that follows the River Rauvin, and absolutely needs to cross the Moon Pass Gorge to get on the other side of the Nether Mountains to the Sundabar Vale. Needless to say, our PC will never even get close to Sundabar, for the adventure will lead him / her in the wildest lands of the south-east Silver Marches and in the Anauroch Desert.
For this reason (primarily, but also to introduce other quest-lines), the Moon Pass Gorge needs to be dramaticall shut, so that even the most stubborn PC is forced to a detour in south-east Luruar, where another trail allows passage through the mountains, the infamous Turnstone Pass, abandoned since the fall of southern Hellgate Keep. Of course, by the time he / she gets to Turnstone Pass, rumors of fiends in the Sundabar Vale shall be the last thing on the mind of our PC.