Doug McCrae said:
So what is the purpose of all these rooms that contain nothing?
"Nothing" is very rarely literal, of course!
No monsters or traps is the key.
Rooms through which one need not fight one's way permit maneuvering. A solid line, by contrast, reduces the affair to something more like the trenches of the First World War.
The latter may be just what one wants if the concept of the game is of one "combat encounter" after another -- but that is not the old dungeon game.
It seems to me that a lot of time is going to be spent describing rooms that contain nothing of importance.
How much time does it take to say, "This little cavern looks like the trolls' midden, piled with bones and rusty armor. There are passages to the north and southeast."? It takes me less than a minute. If players want to spend more time getting more details about something, then it is --
by their own valuation -- of so much more importance.
It's a "free market" of time-valuation, not a DM-driven "planned economy".
Twenty minutes of fun packed into four hours.
That's like the assessment of the guy who took his gal dancing just for the sex afterward. The lady's view? That might be
quite different!
If you consider exploration not fun, then there are plenty of other games for you to play.
The ideal is not hours of constant high tension, but rather a flow of rising and falling tension.
It's hard to pin down a "typical" session, but here's something to give you a rough idea.
The expedition could pass quickly through areas of little interest, especially when covering already well-known ground. One reason for multiple ways up and down is to reduce the need for that, though.
Including time spent that way, and in discussion, etc., we might end up spending about 10 minutes per especially interesting but 'empty' newly discovered room. In other words, we are not necessarily spending 10 minutes poking around that one room! It's a rate or pace. Half a dozen of those would account for an hour total.
Likewise
including activities "framing" it (lead-up and aftermath), we might spend 10 to 15 minutes per minor encounter with monsters (wandering or otherwise), or with a trap or puzzle. Four to six of those would make for another hour.
Figure, say, half an hour for a major encounter. Since an actual fight in old D&D is not likely to take that long unless it's a very big deal involving high-level characters, "major" is more often distinguished by the non-fighting activities involved. A couple of those would take an hour.
So, all those mixed together could add up to three hours. Add another hour for socializing before, after, and along the way, and you would have a session of four hours.
Adding up the above, we have 10 to 14 discretely noted situations -- an average of 3 per hour over 4 hours, or 4 per hour of "knuckling down" to the game (vs. socializing).
YMMV big time -- mine sure does! The group I'm in now definitely spends more than 25% of the time in socializing. A fight that could take just ten minutes to complete in really "serious business" fashion might get stretched to half an hour from start to finish because of all the chatting along the way.