SOLVED. MG or children's sci-fi book with purple light in a mountain [s]

[Padmini]

Some children discover something strange (illegal?) in tunnels in a mountain (?) and there's purple light involved somehow. I also think there were vicious birds attacking them right outside the mountain, but I might be wrong. It's possible that the whole adventure took place on a single night. I read this book sometime between 1999 and 2003. It was published by Scholastic and was the first book in a series or a trilogy. Probably science fiction. The cover showed the kids/mountain at night and definitely had purple light on it.

[Adele]

I'm not sure, but the time and publisher are right and it's the first book in a series:

This book is about a castle, but the cover picture looks like a mountain to me.

[Padmini]

Thanks, but no, it's not the Seventh Tower series. The book I'm looking for was set in the real world (albeit with some sci-fi stuff going on), not a fantasy one.

[Ann aka Iftcan]

The White Mountains possibly? It's been published about a bazillion times, and in different languages, so it's possible it's your book? Maybe?

[Padmini]

No, I don't think it's the White Mountains. But this series looks very interesting - I'll check it out, thanks!

[Daphne]

I keep thinking of The Weirdstone of Brisingamen. It actually does have two sequels, and definitely includes tunnels under a hill. Published many times with different covers.

[Padmini]

No, I don't think there were wizards and dwarfs in it. It was definitely more science fiction than fantasy.

[Adele]

Is it this?

[Padmini]

I think it is this book! Thank you so much! The memory of this book has been haunting me from ages. I shall have to reread it now. Thanks again!

[Adele]

You're very welcome. :-)