El agua es cristalina y están decorados con hermosas estalactitas...

It never ceases to amaze me how I keep coming across things that I haven't seen/noticed in the course. This happens most often when I keep repeating the same mistake like in the above phrase. I keep wanting to say:
- El agua es cristalina y son decorados con hermosas estalactitas...

I'm guessing that "estar" is used because the adjective "decorado" implies something transitory?
 

¡Hola Steven-W15!

Thanks for your question - and my apologies for the delayed answer!

You are right: estar is used for things that are not permanent, and so its use here implies that the many things adorning the caves are temporary or changeable. To use ser would make it seem as though they were permanent. 

Keep up the good work!

- Liss

Gracias, Liss. Había parado de hacer preguntas aquí. Me alegra que tengamos un "tutor" nuevo en el foro ahora. ¡Bienvenida!
 

De nada, Steven-W15, y ¡gracias por la cálida bienvenida!

No dudes en hacer preguntas aquí en el foro - voy a controlarlo frecuentemente.

¡Hasta la próxima!

- Liss