There have been rumours of a hidden chest containing a book with a preview for Ultima 9 among other magical equipment. This chest was supposed to be behind a wall beside Xavier's bed, on Argentrock Isle.
Originally, this rumour was addressed by Jeff Abramson's walkthrough and FAQ, which can be found found in many places listed in my Other Walkthroughs section, which dismissed it as a hoax:
1. Where is the U9 preview chest?
Nowhere, the developers claim there is no such thing.
Underworld Dragon also agreed it was a hoax, and wrote the following in his Ultima 8 Collectibles page:
Underworld Dragon wrote: And although someone has recently reported seeing an Ultima IX preview chest in the game, I've checked the filestamps on this CD and none are later than mid-1995.
Both Kobra Kai and I hackmoved Xavier's whole house to verify whether the rumours were true, but found nothing.
Everyone seems to agree that the Ultima 9 Preview Chest is a hoax. However, there has been one interesting update about it. As Stefan Gruber pointed out, Jeff Abramson eventually updated his walkthrough/FAQ as follows:
Jeff Abramson wrote:
"Where is the U9 preview chest?
For over three years, I have been saying nowhere, the developers claim there is no such thing. However pdick@marathon.Lakeheadu.Ca reports that he did find the preview chest (Oct 97). On argentrock isle in xavier's house there is a wall beside his bed. Use the cheat and move the wall and there is a chest, in the chest are his focuses, and one for ressurection, a bunch of potions, 2 scrolls, a magic helm and level 2 magic armor, and a book with the preview for u9. He cannot confirm if this is in all versions. I have since long uninstalled the game, so other players, let me know!!"
Jeff Abramson's walkthrough/FAQ was updated only on his website, and other copies on the internet do not have this updated information. Unfortunately, Jeff's website went down with Geocities, but an archived copy of his walkthrough/FAQ has been found on the Internet Archive.
This information is interesting because it gives more information about what the Ultima 9 Preview Chest supposedly contains; however it still does not hold water against the verifications that Underworld Dragon, Kobra Kai and I carried out - as well as the fact that, as Kobra Kai noted, there exists no level 2 magic armour in the game.
There is a unique and seemingly useless item - a blue vial that cannot be used - in the Fisherman's Reef area. The vial is located on a bag on a skeleton in a cave behind the waterfall in the north part of the area. It has no in-game label and nothing happens when you double-click it.
The blue vial is also mentioned in the U8 Nitpicks page at The Codex of Editable Wisdom.
In October 2009, Stefan Gruber told me about a special kind of Executioner's Hood, labelled as "sliced executioner's hood", found in the Upper Catacombs. Like the blue vial, this is a unique and (apparently) useless item.
Kobra Kai confirmed its existence and sent a screenshot along with clear instructions about where it is located:
Kobra Kai wrote: It's on a dead body located along the path to the Necromancer who teaches you the spell Withstand Death. There a chest nearby and a fire dart blower (which quite possibly killed the warrior).