I hit the kill switch, and the engine shudders to a halt at the same time I do. I'm intact but shattered.
The trip looked easy enough on paper, but the bike's too big for us. And we got lost looking for the bridge, cringing every time we had to u-turn on tiptoes. Once we found it, we missed the turnoff to the "main" road, and I had to share a tiny trail with local children on pushbikes, pulling over - still on tiptoes - to let them through.
Even near the cave the signage wasn't clear, and we ended up on a steep, narrow quarry trail which eventually petered out, leaving me flipping up my visor and yelling "where the hell is the road?". While I attempted a u-turn on fist-sized rocks, Lyn hopped off: if we're both under the bike, who's going to pick it up?
Between us we kept the bike upright, but there were a few scary moments. Soloing down a steep incline - Lyn was on foot, because down is always worse than up - I nearly lost it on a series of huge rocks. And, of course, every single time either of us needed to get on to or off the bike was a challenge.
The caves themselves were also challenging. We had them to ourselves, with dim LED lights and high-pitched ringing in our ears. One required a ten-metre climb up a bamboo ladder that creaked underneath us. It also featured a cave spider - the size of a huntsman, but infinitely more frightening.
Back in town at Vang Vieng, I'm mentally exhausted, with the same hollow feeling in my head that I get after hours of heavy programming. At first I'm surprised by this. But while the conscious 15% of my brain was screaming into my skull and struggling to control the throttle, the rest was doing heavy physics. As it turns out, it wasn't doing it for free.
It's not just that I'm tired. It's that I'm not recovering. Coffee and lunch don't help. I crave alcohol and sugar - not unusual, but the magnitude has changed. Lyn pinpoints it: the feeling's the same as the aftermath of rescuing the drowning man at Tioman. It's the aftereffects of an adrenalin dump. The only thing that will help is sleep, and that won't come easily.
Before bed, I walk back to the bike to check the trip counter for today. Twelve kilometers.