I leave the best for last, and that honour belongs to Deer Cave, holder of superlatives. It does not need cissy stalactites or stalagmites or what-have-you-ites to make it famous, it just needs to be physically awesomely huge!
You can’t imagine the hugeness of the passage until you realise that, as you near it, you can’t find the normal gaping mouth of a cave.
You just keep walking … 
… and walking …
… and noting a stream from nowhere going to nowhere …
.. and walking, and then, you start realising there’s less and less light. Is there an eclipse of the sun?
The odd bat appears, one of the 12 species domiciling in this amazing cave. It’s a small critter, can fit on one’s palm easily. One of the millions seen yesterday. 
And suddenly you are staring at a truly cavernous hall, which makes humans (bottom left) look like ants scurrying around.
As I glance back, I realise I am already engulfed by Deer Cave, whose entrance is the world’s largest.
I’m in a gigantic chamber, partially lit by the sun, 175m across and with ceiling 130m from the ground. My jaw drops. Note little folks bottom left.
Even my 17mm camera lens cannot capture the high ceiling! Heck, I can’t make out the ceiling, and soon my neck aches from craning too much. Again note people bottom left.
On one side, dropping water from the leaking ceiling makes a glistening confetti-like show. Very pretty.
As I walk past it, I get a different perspective. Only when it rains you get to see this wonderful sight.
It’s like a very skinny waterfall, falling more than 100m from the top.
There’s even a stream in the middle of the chamber. 
A stony one. In fact I see two streams meeting at the spot beyond the bridge.
Then I enter the darkness of the cave, with the dimly-lighted footpath my only guide. The unmistakeable odour of bat droppings fills the air, and the ground feels soft due to layers of the yucky stuff. There are bats in every nook and cranny, but in the darkness, nothing could be seen, until, …
… we come upon the surreal Garden of Eden …
… formed by the collapsed roof of Deer Cave. In fact this marks the end of Deer Cave proper, and we have just walked the longest cave passage in the world, almost 2km of it.
We make a U-turn and walk back to the cave entrance. With his torchlight, Jerry shows me the glowing worms feeding on the bat guano plus some other creepy crawlies making their home there. And I’m still astounded by the sheer size of the chamber!
I feel like looking across a subterranean world, complete with mountains, hills, rivers, rocks and valleys. If the Rebel Alliance needs a base, Luke Skywalker will choose this spot.
As I look at the entrance, somebody familiar shows himself up.
Mr Abe Lincoln never looked better.
I reluctantly walk out of Deer Cave, I’ve fallen in love with it …
… but Jerry has to switch off the power supply at 5pm, leaving both Lang Cave and Deer Cave in total darkness. I trudge along.
Being a truly memorable day, and what a great guy Jerry has been, we do a little photo at the entrance. If you are reading this, Jerry, thanks a lot!
Soon after, the sky opens up, and I guess the bats won’t be dining out tonight. We promptly return to Park HQ in jungle rain with neither raincoats nor umbrellas. Luckily my camera bag is waterproof. 🙂
40min later, we are safely home soaked to the skin, and our drenched gear get to spend the night under the fan, running at full blast. We have walked some 18km today, at all 4 cave sites.
TO BE CONTINUED …
PS: Nice map of Mulu caves can be had HERE.