That's not from Alan Watts afaik, it's from Robert Pirsig in Zen and the Art of Motorcycle Maintenance.
Discussion
Currently reading 🤓 
Certainly one of the best books I've ever read.
As a young adult feeling lost and misunderstood in my mid-20s, it helped me a lot and later I read it again several times.
I reacted to this post because “The only zen you’ll find on mountaintops is the zen you bring up there with you” immediately stuck with me on my first reading of the book and I keep thinking about this sentence pretty often.
How do you like it so far?