The first two things you encounter in Bonechill Passage are a wolf and several cleaned skeletons. Get the lupine out of your face and you can advance to the first chamber, which holds still more dead- including a relatively fresh adventurer corpse. Take the potion of healing lying against the dead man and anything in his inventory or the nearby knapsack that suits your fancy, and read the book in the middle of the room to increase your Heavy Armor skill one rank. As you move to exit the room, an Ice Wraith will attack- these things are annoying but should be little more than a nuisance- they -are-, however, virtually impossible to properly hit with a bow and arrow or single-shot spell.
Up the next passageway is a room with a stone bridge, which is topped by a live Frost Troll. Take it out, then check the remains of its meals for some gold, bonemeal, and a strong stamina potion. After the troll is the last tunnel of Bonechill Passage, which takes you out the top of it and into Ancient's Ascent. Be wary as you top the stairs- the dragon is watching you.
Pick any way you like to get the creature's attention, and you can immediately start using the terrain to your advantage- if you're uphill from the dragon, you can choose between the open tundra atop the mountain, the light woods nearby, or the craggy area around the mountain road. If you came from Bonechill Passage, you're in a rather open area with little cover- but that may be to your liking if you'd rather face the dragon sword-to-tooth.
This is pretty much a typical dragon fight, though the dragon here tends to be of lower level than the dragons you face while out and about, making it a touch less challenging. Once you've slain the thing, you can approach the Word Wall it was sitting on to learn a word from the Animal Allegiance Thu'um, which calls wild animals to aid you when used.
A decently-stocked treasure chest also waits for you in front of the Word Wall, so rummage though that as well.
If you want a bit of additional amusement, the rocky crags in front of Ancient's Ascent provide an excellent view of the now-ruined Helgen, suggesting that this is where the dragon that destroyed the town was waiting originally.
