trip to Iceland... what to do?

Yes, the Blue Lagoon is fantastic. The one thing that I regret on my trip was that the Blue Lagoon was included in a full day excursion and we only had a couple of hours here. If I ever go back, I'll do the entire day.

I also recommend doing the Golden Circle Tour and take one of the whale watching cruises. There are minke whales and dolphins everywhere. During certain months they also get a lot of puffins, which are kind of funny.

Have fun, and be prepared to spend a lot of money. There is a huge difference in cost of living in Iceland, and everything is very expensive.

Oh boy, 3 days? That's nowhere near enough for Iceland. Take a look at what I had planned for Iceland and I was there for 9 days, each day busy, yet I only got a chance to see a little. And luckily for me, I had 22 hours of daylight available so I went until the middle of the night as it was still bright as day:

http://www.markiniceland.com/planned-itinerary/

Blue Lagoon is not as good as it looks. It's much, much better. You can't put that in pictures. You'll be blown away. There's a cave that's heated by those sulfur rich, natural steams which will have your jaw dropped, the waterfall you can stand under, silica mud from the bottom of the lagoon is provided in crates so you can apply to your skin (has amazing cleansing and rejuvenating properties and is as fresh and as pure as they get). There are no words to describe how awesome Blue Lagoon is. However - it's also extremely expensive. It costs 3400 ISK. Iceland is an expensive country overall.

Take a look at my projected itinerary, it might inspire you into what to do. Pick what appeals most to you. Iceland has a little bit of everything. You could go on an ATV ride on a glacier, or go whale watching, or climb a volcanic crater, or scuba dive in waters surrounding ruins, or go take pictures of puffins (actually no, not in November - I went in June, during their nesting season), or walk behind a waterfall with 60 meter drop... there is so much to see and experience in Iceland it's out of this world.

Golden Circle would be a good option. It's close to Reykjavik and can be done in one day. You'll see the geysir, including the still erupting Strakkur, Golden Falls and Thingvellir where world's first parliament was established in 9th century.

go ice fishin