In the average player's mind, Guild Halls are often a place to chat with guildmates and have guild meetings, etc., and that's something I agree with. But everything can be spiced up a bit, so let's go through my list of suggestions for the Guild Halls of Spiral Knights.
Guild Sparring Chambers:
A basic place for guild members to practice PvP related things, simply learn how the games work. There are no payments or rewards for/from matches in the Guild Sparring Chambers. Requires F5 West Wing upgrade.
Price: 50m Crowns
Guild Training Hall Upgrades:
Now, the Guild Training Hall can be upgraded to have sections for testing Quickslot Items, practicing Scenario Rooms (only the ones with enemies, and those enemies give rewards equal to the amount you'd get killing an enemy at Depth 1 on normal difficulty), Arena Rooms for all monsters (also no rewards, as they respawn), a Depth Selector (for all 29 floors, opens a GUI, which replaces changing tiers),special boss rooms (no token, crown, heat or item drops, just for practice, it's a training hall people) and even a Training Hall Design Mode!
Upgrades only require a Guild Training Hall.
Prices: Quickslot Room: 1m Crowns; Scenario Room Selection: 15m Crowns; Enemy Arenas: 100m Crowns (with the Design Mode, you can arrange the spawners as you please); Depth Selector: 50m Crowns; Boss Room: 10m Crowns (Snarbolax), 15m Crowns (Royal Jelly, Roarmulous Twins), 25m Crowns (Lord Vanaduke), 100m Crowns (Shadow Lair Bosses + Unknown Passage, but not The Sanctuary); Design Mode: 500m Crowns
Sanctuary Alchemy Room:
Unlike other rooms, you don't buy it, but you craft it, using 10 of each of the Shadow Lair materials, 50 of every other 5 star material (not including event materials, obviously) and 25m Crowns. You can only craft armors/helmets using SL materials you obtained yourself (now Shadow Lair materials have an "Obtained by " tag, which determines usability for the alchemy machine in the room. You can still use the ones that weren't obtained by you at the alchemy machine in The Sanctuary), to prevent easy obtaining of said armors/helmets.
Apocrean Theme:
For those guilds that love dark, grim settings. Harmless Lost Souls and Apocrean Harvesters will sometimes appear briefly.
Price: 100K Crowns
Sanctuary Theme:
Life has sprung anew after the swarm was pushed back, so you can live happy, at least for now...
Price: 250K Crowns
Whitespace Theme (+ Whitespace Environment):
Not actually a selectable theme. This theme is used for guilds in default. The Swarm infests the Guild Hall, slowing down knights by 5% (percentage small enough to hopefully avoid causing ragequits [slowdown is given by the theme, not the environment]).
Whitespace (Environment):
This Environment, unlike the theme, is selectable and makes the area look as if the swarm infested it (no slowdown included).
Price: 90K Crowns
Teleporter (Furniture):
Now, we go hi-tech! As the name (and every film/game with one in it) implies, you can use these to quickly traverse the guild hall. A GUI appears when interacting with one, displaying the locations of all other teleporters on a map of the hall, indicated by a green dot that when clicked on, moves you to that teleporter.
Price: 1m Crowns (first buy gives two)
Wolver Den:
This room has 7 friendly wolvers wandering around inside, because everyone loves dogs!
Price: