From ErfWiki

Proposed Canon

Minnow Tower was the Tower of Garrison in the capital city of Goodminton around the time when Wanda popped.

It is described as being "a somewhat taller gray rectangle than those that comprised the rest of the Garrison." Tower's top was manned with archers and ballistas for air defense, but poorly protected with air defense spells.

The Tower hosts the war room, as well as Overlord Firebaugh's quarters, private office, and public reception on the floor above it.

Speculation

According to Delphie Temple the Tower offers very insignificant bonus for spell casting.

Delphie's claim may only be an excuse for choosing the Dungeon as her quarters and refusing to protect the Garrison with air defense spells.

Real World References

The name is a pun on "minotaur".