Stefan Popov
Google
I found it a bit expensive, maybe it's just subjective, but I think it could be a bit cheaper. It's a very cool trip, they pick you up (and return you to) the city centre, you get a theoretical presentation about Inca geography, astronomy, and agriculture at first, followed by a virtual sky presentation in the dome, and finally, using real telescopes, you try (this is dependent on the weather) to find and observe some star constellation, and the planets of Mars and Jupiter. Cool and alternative trip compared to everything else offered around, and you learn a lot of interesting stuff!