Location is basically under the bridge in Colle Val d'Elsa. There's no building as such so park up in the nearby car park and walk to the bridge, stopping at the nearby bar for a toilet break if required.
Our guide was Alessio (excuse spelling), really informative for the history, geology and myths of the river and even convince a reluctant member of our family to jump in on our river trekking adventure.
River trekking was great, lots of jumping in but only from low heights, max 1m and everyone in the family enjoyed the experience, thoroughly recommend it.