The way ahead is certainly not safe in any way, but the party has no choice but to proceed if they are to accomplish their mission.
The tunnel branches ahead more than once, but most of these prove to be dead ends. As you travel, you hear stony clicks at various times, and knowing that this means that the boulder-creatures are near you proceed cautiously, but you are not confronted and there is little point in attacking every rock on the chance that it might be an enemy.
You are all tired. It's hard to keep track of time in the tunnels but it certainly feels like you've had more than a day of travelling. The party sets up camp, with a meager dinner consisting of game caught before you entered the tunnels.
Throughout the 'night' there are numerous odd noises and stony tapping, but you see nothing causing it. When you feel you have rested enough (for there is no sunrise here), you resume the journey.
Finally you see light at the end of the tunnel. You emerge into a large sunlit valley. Across the valley are yet more mountains, though. Father Fuller is not too surprised by this, as he'd heard that there are valleys within the Great Pass that must be crossed before entering yet more tunnels.
This end of the valley is a broad plain, very level and free of stones. The grass appears to have been neatly cropped so that it is no longer than 2” in any place. Small brooks criss-cross the valley. Their banks are very soft and marshy. No trees, buildings, or other cover are in sight.
Girgal notices horse tracks as the party crosses one of the streams. There are small fish there as well.
After about a mile of this, you see a group of about half a dozen creatures ahead. They appear to have the bodies of horses but with humanoid upper bodies in place of the horse head - centaurs. They gallop away.
Soon a larger group of the centaurs approaches, about 15 of them. They are armed with composite longbows and lances.
The lead centaur, a male, hails you warily. "Greetings, travellers. Who are you and what is your business here?"