I've come across something unusual in Witcher 3, a couple of times recently and would be interested if any has information.

The images are from Dragonslayer's Grotto, in search for Griffin School Gear.

At the very end is a wall. Normally it looks like a large boulder, except its shimmering.

When I enhance it using Witcher senses, it has the familiar yellow outline indicating something and a strange symbol, like a star or similar.

I've seen this in other caves elsewhere.

I tried a bomb and Aard but to no effect.

Looking in the various Wikis, I found nothing at all.

Anyone?

I won't spoil it for you, but advancing the main quest will answer your question.

Yes, as k4ZE106 says, you need to advance the main quest. In particular, a very early main quest.

***** SPOILER *****
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Click link for spoiler.

Got it now. <blush>

Thanks tons to you both for responding.