the side trips 1: india and the himalayas

I'm starting to fill in the detail of the bits in between the main flights. I'm arriving in Delhi on 10 November and flying out over a month later, and the plan is to go to Nepal and Bhutan, where I have reserved a place on a trek with Himalayan Kingdoms, the experts in trips in those countries. The detailed itinerary is similar to this. Bhutan is not an easy place to get into as an independent traveller so it seems like a good idea to go on an organised trip - not to mention it's billed as a 'gentle trek' where they carry all your luggage for you and you stay in well appointed accommodation. I hope their idea of gentle is the same as mine!
Bhutan has always fascinated me. There's something about those remote little independent states, the flotsam and jetsam of nationhood, that I have always been attracted to. (Places like Andorra, San Marino, Liechtenstein also come to mind). There is also the sense that Bhutan is a Shangri-la that carefully protects itself from outside influence. I expect to see some amazing sights.
I do want on this trip to get to places I would never have the chance to visit ordinarily.
Other ideas when I am in India (map) are a trip to Jodhpur and Jaisalmer, in the far north west of Rajasthan. I have previously visited Udaipur and Jaipur, which were fascinating, but Jaisalmer in particular seems very remote and even has sand dune deserts nearby. Ian recommended this trip - and I would love to go around on the Indian rail system if that is possible. I had a limited experience of this (Mumbai to Pune) and it still seems to be one of the transport wonders of the world.
As I only have about 11 days before leaving for Kathmandu, and about 4 days after returning, I will have to be careful not to cram in too much. But I am also thinking about going to Goa for the few days after Kathmandu. I'll wait to arrange this until I am there, though, in case I decide to rest in Delhi after the trek.
Another idea would be Chandigarh, which is close to Delhi and famous for its le Corbusier architecture.