The PCs recently wrapped up a four-session jaunt through a gate to the Gardens of Trent Oakheart, also called (by the PCs, mainly), "The Garden of the Masters."
How I thought it would go:
The PCs arrive and realize there is no immediate gate back out. They search the area to ensure that, and search the area to be sure there isn't a gate there. They find the staff and seal. Quenton has a vision and knows the nature of the Garden and the threat . . . and has a critical tool to cleansing it. They'd cast a bazillion spells to check as much of this as they could, use Know Location to determine they weren't anywhere in their own world, etc.
They find the nearby pool - it's not obvious but a narrow path like that is a sure call to curiosity if you know there is a supernatural spirit-pool nearby. Armed with the spirit from the pool, they'd have both parts of the formula necessary to cleanse the place. They wouldn't know more than vaguely where to go, since the spirit couldn't communicate that and Trent Oakheart's lingering spirit couldn't know where he was to direct them.
The PCs would spend a session adventuring around, probably seeking loot as well as seeking the evil tree. They might realize the vegepygmies were potentially friendly, or fight them.
That would probably be most of a session.
Session two would be finding the tree and defeating it. That would take some time - lots of potential fights, and with a lot of ground to cover, there was a risk of spending too much time wandering off in corners trying to find more loot or "just make sure the tree isn't over here."
But yeah, two sessions.
Of course, that's not what happened.
The PCs arrived, and were totally unimpressed by the lack of a gate. Weird vegetation land? Show me the money! They cast Seek Earth to find valuable materials and located a magical jeweled sword. They made a beeline right there, going so far as to carve their own path through rotten vegetation to find it. They eventually did and alerted the evil tree to their presence by setting off the garden's inherent response to fire attacks - kill the offenders, rain on the fire (which wasn't needed in the end.)
They spent a good solid session on loot and finding more. Then they spent a good chunk on getting it and then fighting the tree. The path from there was, ironically, lengthened by their attempts to shorten it. They almost went all the way back to the start, but then decided it was a waste of time to start there instead of starting here.
All told, it was a great set of sessions. No one griped about the length, or worried about XP. They were fascinated byt the place. They joked about how they lived there now, and how they'd survive on squash and live with the vegepygmies, and how it was all the startship Warden from Metamorphosis Alpha.
But it's amusing how I set it up as an easy "do the thing" adventure with minimal "find the thing to do the thing" elements. Yet it turned into a mystery - what is this place? How do we leave? What's it all mean? How do we defeat this unkillable enemy? All, basically, because no one looked around or behind them when they arrived.
Amusing, really. Even obvious clues are not always obvious enough!