Final Quest

"The Castle of Shadows, I think," you say.
"All right. Get on my back."
You do so, holding on awkwardly. The green dragon spreads his wings, and lifts into the air.
The dragon flies to a huge black castle. At least, you assume its a castle. It doesn't have a drawbridge or a moat.
You get off the green dragon. He turns his head to look at you. "I'll go in first," he tells you.
You nod, but eye the entrance to the castle with some apprehension. After all, it hardly seems big enough to allow a dragon to go through.
Next to you, the green dragon laughs a little. You look at him, and he suddenly shrinks down so that he's just a little taller than you.
"How did you do that?" you gasp.
"Magic," the green dragon answers, a trace of amusement in his voice.
You and the green dragon enter the castle. However, no sooner are you in then you hear a creaking noise, and the door behind you swings shut, plunging you both into darkness.
You take a deep breath, and manage to stop yourself from running over to the door and banging on it. "I think it may have been a mistake deciding to come here," you say.
"That's all right," the green dragon replies. "I don't hold it against you."
There is a flicker of light that grows steadily stronger, and you realise that the dragon is glowing enough for you to see your way.
After going forward a little way, you come to a wall. However, there are stairs going up, and a staircase going down.
"What do you want to do?" the green dragon asks.
Go...