Floor 21
Belweir: Welcome to my library!
Floor 21 is a (dark) cavern which contains Belweir's Library. This opens into a small entrance room, with a magically sealed door leading to the Library proper. The entrance room features four rows of four fiery altars, which can be used to unseal the door. The library itself has reinforced walls that cannot be dug through, and you are prevented from teleporting inside -- the only way in is through that door.
To open the door, you need to place the appropriate combination of items on the fiery altars. (Before you start, pick up any random items!) The puzzle is a variant of Sudoku: Each group or four, each row, and each column, should have one ring, one wand, one scroll, and one potion. It doesn't matter what the particular types of items are, if they "match", whether they're cursed or blessed, or if the wands have any charges left. Note that bottles of water do not count as potions, but Wands of Nothing and Wedding Rings do count.
When you attempt to open the door, any items that are in the right place will vibrate, while any other items (random or misplaced) on the altars will disappear. (Pick up anything you might want from the altars before trying the door.) When all 16 altars have the right item, the magical door will open. It will also permanently change into a normal door, so at this point you can reclaim any or all of the surviving puzzle items.
The best way to figure out the pattern is to start by placing a single wand on any of the altars, and then trying the door. If it disappears, try another altar in the same group, until you get the right position for the wand. (You should have plenty of wands to sacrifice if you went through the tridude level.) After that, go to your next most plentiful item, and continue until you've gotten the first group. Then proceed to the group diagonally opposite from the one you've solved, and try a wand. It will likely be in either the same position as in the first group, or the opposite corner. Continue as before, and you'll eventually get all the items in their proper place. Note that for your "last" item type, you only need four (which you'll be able to get back afterwards), and with a little thought, you can do almost as well for the next-to-last type. (You needn't actually finish the second group before placing wands etc. in the others.)
The exact pattern needed varies from game to game, but always follows the rules above. A couple of examples:
| A | B | C | D | |
| D | C | B | A | |
| C | D | A | B | |
| B | A | D | C |
or
| A | B | C | D | |
| C | D | A | B | |
| B | A | D | C | |
| D | C | B | A |
Observe that each row, column and quadrant contains one of each item.
Inside the library are numerous scrolls and tomes. You will probably end up with at least one of everything (except a Scroll of Omnipotence). There is also a hole you can use to drop down to the next floor. This is very useful if you've got a bunch of unused skill/spell points because you haven't found the right books. On the other hand if you already have plenty of spells, skills, and scrolls, but not many potions or rings you're willing to gamble with, it might be best to bypass the library entirely.
