I was playing keeper and I interpreted the explore action as a single card revealed per action. Where a stack of three cards at one location had to be explored 3 times to reveal all cards. Another player interpreted the rule as all cards are revealed and taken by the exploring player if the lock or obstacle cards are solved or there aren't any there. Which is correct?

I am pretty sure it is all cards.

Yeah, it's all the cards.

All card - see page 9 of the Rules of Play section at the top of the right hand column. The Explore action information actually start at the bottom left, but what you are looking for is at the top right.

It's all cards, one at a time, unless the cards tell you otherwise. I don't think the last part is likely to come up unless an investigator drops some equipment cards on top of an obstacle card, but I imagine the rule is in this way to allow for future scenarios to have face down items found "freely" and then have a locked suitcase/cabinet/closet/etc. with the remainder "hidden" behind it.

Awesome guys, thanks.