CONFIRMED! Note: This can ONLY be done during the first few chapters. If you get to the Gathering or the Summit, you've missed it.
Pick up the broom in Stinegard (or however you spell it), from the blacksmith. Look at his wares (in the shop, NOT the buy/sell menu), then start to leave. Do NOT buy anything. If you do, you WILL fail.
If done right, he will stop you. He will tell you he only has the handle. Buy it (1,000 Sx). Next, go to the forest in the west.
Might be random, but for me there was an encounter with a traveling succubus five tiles down, three from the left. She offers you a choice. Choose "Fight". After you win, she gives you the brush.
Go to the Mage Tower, and visit Robin. Talk to the three girls (any order), then visit the other rooms IN THIS ORDER: Chapel, Library, Study Hall, Chapel again. You don't need to speak to anyone, just go in. Now try to enter the boy's dorm. You'll be stopped, but that's fine. Go back to town.
Visit the brothel, and talk to the madam.
Go to the succubus shop, and look at the wares (again, NOT the buy/sell menu), and, again, start to leave WITHOUT buying anything. You'll be stopped, and given the option to give them the handle and brush. KEEP THEM! If you give the pieces, they keep the broom for themselves!
Now go back to the blacksmith, and give him the handle and brush (you can only do this after going to the succubus shop). He'll charge you a further 1,000 Sx for it. Pay him (if you have it), and he'll take the pieces. This is the ONLY chance you have to do this, so make sure that you've got 1,000 Sx. One brief cutscene later, and you have A Like-New Broom.
Go back to the bounty board, only to find that the original bounty is gone! Go to the inn.
Talk to the innkeeper, and he'll offer to buy the broom for 10,000 Sx. Take it if you want, or hold onto it a while longer.
If you've held onto it, go to the magic shop, where the storekeeper will offer to enchant it, for free (a very good price), as a way of testing his skills. Say yes. You now have a Shining Broom!
Now, go ALL the way back to Simon's hut. Yes, the one from the beginning of the game. Look at the portrait of Wendis, then go to the Chapel. Speak with the Roaming Sister. Celebrate, as you're almost done!
Continue the game as normal, until you get to Ari-Yilhin (or however you spell it). Take the Shining Broom to the Merchant's Quarter. IF you've done everything correctly, there will be an old man roaming around the south part of the area. He'll offer "something wonderful, but of little worth to those with imagination". Say "You've got a deal, Old Man."
Save your game here, and quit to the main menu. Then choose "Continue", and load your save. Under "Settings", there will be a "Something Wonderful" option. Toggle it. CAUTION: Be absolutely SURE you want to do this, as this CAN NOT be changed. If you're sure, say "Yes."
The game will appear to glitch, showing a white screen, then a black one with an eye in the center, followed by the letter "D", then one, followed by zero, then a cross. It will then shut itself down. Don't panic, boot it back up, and load your save again.
Congrats, you've unlocked the rendered 3D scenes! Enjoy!