A general map of the five mile hex in which Rhuun is located. Labeled are A) Rhuun, B) The Tomb of Athkul, and C) the dry river that heads into the Hills of Scowling Bones and leads to the Temple of the Goat.
Traveling on foot through rough terrain with party members in metal armor means you can cover a mere 8 miles a day (Base overland movement rate is equal to turn-based movement rate divided by 5 in miles, so a movement of 60' [metal-wearing PC movement rate] divided by 5 equals 12 for 12 miles per day overland. Desert, hill, and mountain terrain reduces that by an additional 1/3 which becomes 8 miles/day). This is why it takes a day and change to reach the Temple of the Goat. On horseback or muleback, you can cover the distance in less than a day (something to think about now that your coin purses are flush).
Due to the rough terrain of the Hills of Scowling Bones, it would be difficult, but not impossible, to reach the temple via wagon. Hiring a teamster to drive the wagon would reduce the chance of mishaps but you'd have to find one willing to risk his life and possibly his team to journey to the temple. Organizing a mule train is another possible method of retrieving the sizable library from the pyramid and returning it to Rhuun. At bare minimum, which would require the PCs to carry their own gear so as to free up Gladys and Doris to haul nothing but books, you'd need at least one more mule. This would mean that each animal would be bearing their maximum load of 400 lbs. each and leave no room for error in case one gets injured or eaten. Additionally, they'd have a movement rate of 60' (the same as you on foot), meaning it'd be a day plus trip back. Purchasing three more mules to bring the party total up to five would allow the mules to make the trip back in under a day but would still leave you no room for error in case one mule became injured. You'd also have to provide mounts for yourselves if you wanted to keep pace with your pack animals!
This is a continuation into the neighboring hex to the north. There is a slight gap between the two which is indicated by the blank northernmost hexes in the first map. I'll have a better version together before next Sunday's game.