Ha Long Bay
I think I won't say that much about Ha Long Bay. We booked a three-days tour in a travel agency in Hang Bac street for 40USD/pers (food, transportation, guide, visiting fees, first night on a junk, second night in a 3-stars Hotel on Cat BA Island, kayaking, trekking were all included).
So we've done all of this. The only annoying part was the transport from Hanoi to Ha Long City where we took the junk and then it was just terrific. The tiphoon was completely gone and we had blue sky during the whole trip. Visiting the grottoes was amazing. Admiring hundreds of limestone islands was something I was expecting and yet I hadn't imagine something that impressive.
Once again we've done some random things like kayaking at night (we took a kayak to cross the bay and go to the top of an island to watch the sunset, by the time we did it it was complete dark when we had to cross back the bay), did an illegal?? fire on a quay in the harbour close to our Hotel in Cat Ba Island and jumped from the top of our boat (around 5m high) into the water.
Hope you'll like photos because I really enjoyed these 3 perfect days.