Just returned fron 2 week cruise on Independence of the Seas and went rafting in Vigo.
We (2 adults + 12 year old) throughly enjoyed the experience.
The journey to the river took approx 1 1/2 each way and we had 2 hours on the river.
There are several rapids but other areas of calmer water for water fights!
The rapids are level 1 and 2 and were covered by our general travel insurance policy.
Lunch was provided (eaten in hand at river side) - huge chorizo rolls and bottled water.
It was one of the few 'adventure' excursions on the trip. As a fellow rafter said there was only so many cathedrals you want look at on a trip.
Although trying to book this excursion on board at 2pm on the first day it had already sold out and we had to go on a wait list until additional spaces were provided. It was heavily oversubscribed so book as soon as you go onboard if you wish to go.
Your clothes will get soaked so wear swimming clothes underneath and take a change and a towel (items can be safely left on the bus - nothing can be taken onto the rafts).
The only draw back was lack of toilet/changing facilities at site.
It was one of the highlights of the trip (as it was different) together with climbing the leaning tower of pisa and visiting Rome.