"¿Qué caballo montaste?"
Translation:What horse did you ride?
What would mean that the person is asking about a particular characteristic of horse like colour. what (coloured) horse did you ride?
Why not, "What/which horse did you mount?" Seems a little odd to say, but should work
just wondering, what makes the sentence past tense? i thought it was "what horse are you riding" but it was wrong.