Before doing the Tower of Aroxa, you will need someone who has either the sword or the whip skill to complete it, (Whips for mage classes and swords for warrior classes). Also, once you have completed it you can never re-enter the area.
Preparation
Find the ranger, who's in love with the princess. He wanders around the first parts of the Tower of Aroxa so just wander around until you find him. Sayto him "princess" and he'll give you a key and say something about needing it to rescue the princess. Go to the northeast side of the forest area, from the entrance into the caves with the bats. At the far end of the caves is a black bat with a unique long description. Kill the bat and obtain the cord item from it. From there, go all south, all west, all north, all east, northeast, north and put the cord object into the obelisk. The castle will now open up and allow you to go inside.
Go all west, and turn the sconce. This will open another passage. Go west, all north and you should be in the throne room. Push button and it will open a room to the east. Go in and grab the book, wait in there until it repops if it's not already there. Once you have the book, go west, all south, east until you see an up then continue up the stairs. On the first floor landing, go all south. Unlock the south with the key you got from the ranger and go inside. Turn the jack in the box, which will sometimes take a while to reset and it will spring open and mention something dropping to the floor. Search and pick up the silver tuning fork.
Head north back out of the room and down the stairs, go west until you see the sword and wear then use the tuning fork in the same room as it. A couple of room echoes will happen. Pick up the sword and go east back towards the stairs. If you don't have the sword skill, the sword will turn into whatever the "main" weapon is for your class. Go up until you hit the second level of the tower, then all south and east. Open the box in here, grab the key out of it then close the box to prevent spiders coming out of it. Go west, unlock the west door and go inside. Drop the book and a wizard will appear and mention something about being trapped in it. Once he disappears, go east quickly and pick up two blue potions which have now appeared on the floor.
Optional side quest
Now to get you the item you'll need to get the special objects in the dragon's room. If you don't want these items, which aren't too great after level 100 don't bother doing this paragraph. Go north until you're at the staircase, then all down, all west, all north, west and push the stone. A passage will open down, go down and dig to reveal an exit to the west. Go into the passage and you'll meet the king. A key repops in here rarely, wait in here until you get the key and dig to get back out if you need to. Go east, turn sconce to open up and go up. East, south, east, north, and push button. This will open a room to the east, go in, then up, and turn sconce. The door above will open, go in here and wait for the jar to repop. Once you have the jar, push stone if you need to to go back down, then down again and turn sconce and back out into the throne room. Then go all south, all east and unlock the east door. Go into the room with the pond, wear the jar and use it. (Repeat as needed. You may not get the koi the first time. "You bend over the pond and try to scoop a koi into the jar, but you just aren't fast enough.") Now head back to the stairs.
The Great Dragon Ragzul encounter
Go north until you're at the staircase, if you're not already on it and go up until you see a wall of fire rages in the room; which will hurt you with fire damage everytime you try to go past it. The dragon is directly up from here. Drink one of the blue potions and it will hurt you and take the fire down, until repop. Wear the sword and go up. Attack him and kill him. He is rather tough, but if you're using the dragonslayer weapon, it will do massive lots of damage to him. Try auto defense if you have shield block so you don't die. If you die, resurrect quickly and try again.
Once you slay him, get the key from his corpse, unlock up and go up. The princess will be grumpy and say some rather rude things to you, this will grant the Mark of Dragon.
Note: She'll drop her tissue. If you completed the optional side quest with the jar with the koi in it, wear it and use it. A chest will appear, open the chest and get all from it. Grab the tissue and go back down to the ranger making sure you stay away from the stone trolls in the castle as they instantly slay you. Give the tissue to the ranger and he'll give you a stone bow. It also gives some quest points now. After you kill the dragon, you may also pay the king a visit to get a reward of 50k gold.