When fighting maze in Hook Coast, Go to the hook coast bell. There will spawn a screamer. As you kill it, a new one wil spawn. This process can be repeated as often as you want, and can get you up to 999.999.999 XP. If you do it correctly, you will get a combat multiplier of over 40, so a ages of will, might or skill potion will get you about 300000 XP.