This is intended as a supplement to Pablo's answer.
Let's start with
Se negó, lo cual fue una decisión que resultó desastrosa.
(This is equivalent to "He refused, which was a decision that proved disastrous.")
There is a nice way of making it more concise:
Se negó, decisión que resultó desastrosa.
(This is equivalent to "He refused, which decision proved disastrous," or "He refused -- a decision which proved disastrous.")
Note that this concise version is more common in formal language (essays, speeches, etc.) than in conversation.
If you want to practice making sentences with this pattern, you'll need to come up with a word that describes, or sums up, the first clause. Here are some more examples, with the summing up word in bold:
Cuando empezó a tener problemas con las encías, el niño empezó a lavarse los dientes diez veces al día, práctica que agudizó la inflamación de las encías.
La maestra de matemáticas les encargaba, a diario, 40 problemas del mismito tipo, tarea que le hizo cuestionar su predilección por la materia.
In a comment, you had a similar but slightly different example:
It rained all day, during which time we played cards.
In principle you could say
Llovió todo el día, tiempo durante el cual jugamos a las cartas.
But I don't recommend this. It just sounds unnecessarily pretentious. However, sometimes it is helpful. I'll try to come up with such an example, where it is worthwhile:
La organización X estuvo activa desde (fecha m) hasta (fecha n), periodo en el cual se presentaron varios proyectos de ley que formaron el fundamento de la política actual de anti-discriminación.
You could substitute "durante" for "en." The effect is the same.
Again, I put the summing up descriptive word in bold to make things clearer.