When an opponent's monster declares an attack: Your opponent chooses 1 random card in your hand and calls the type of the card (Monster, Spell, or Trap), and if they call it wrong, return the attacking monster to the hand.
Rulings
Individual Card FAQs
If your opponent calls it right, the attack resolves normally.
You cannot activate "Ordeal of a Traveler"'s effect if you have no cards in your hand.
You can activate the effect of "Ordeal of a Traveler" each time your opponent attacks.
You must show the card your opponent selects to your opponent.
When "Ordeal of a Traveler" & "Fairy Box" are both active, "Fairy Box" (mandatory) is step 1 of the chain, and "Ordeal of a Traveler" (optional) is step 2.
When you activate "Ordeal of a Traveler"'s effect as a chain to "Magic Cylinder", since "Ordeal of a Traveler" resolves first, if your opponent guesses incorrectly then the attack does not resolve and the effect of "Magic Cylinder" disappears. If multiple copies of "Ordeal of a Traveler" are active, their effects are cumulative.
Trap|
Continuous