Where is "home" for you when you're not visiting Seville? Here's why I ask...
I often see folks post about doing various activities while on their trip to Europe. Hot air ballooning, skydiving, paragliding, etc. I'm sure these activities are fun while you're on holiday in Europe. But I suspect that for many of these activities, the actual experience is pretty much the same as it would be back at home (for me at least, "at home" is in the USA - where these activities are much, much less expensive). Back homes, such activities cost justa fraction of what they cost in Europe. To me, it seems crazy to spend 5 times as much as it would cost at home to jump out of a plane over Tuscany, when the experience is not going to differ much from jumping out of a plane over Tacoma. I suspect it may be the same with horseback riding - unless you're doing it in a special environment (on the beach at sunset) it might be better to do it after you get home.
The way I look at it, there are things that are "better in Europe" - museums, art, cathedrals, etc. On my trip to Europe, where the "days there" is the most limited commodity I have, I want to spend those days on the things that are best done in Europe. So for me, jumping out of a plane (or maybe riding horses) can wait until I get home where it costs a fraction of the going rate in Europe, and I'll spend that time exploring a castle, which is much harder to find at home. I do realize that this may be hard to rationalize with a family member who has their heart set on it.
Just my 2 cents.