I passed the whole test on all 3 levels and got my mark and was thus teleported back to the temple level.

Now I realized I forgot to find and get the hammer. So I reentered again the silver towers to get back to level 3, but guess what, the door on level 2 leading to the stairs to level 3 is now locked. How can I get again to level 3???

Is this a dead end I stepped in by accident?? (Please tell me, it isn`t).

If you mean the door which opens when magic mouths' riddles are completed and then closes after Dran's short encounter, I have no idea whether or not that door can be opened again. Perhaps it can't.

That would be a huge game design failure. Nobody told me about the hammer on 3. Level, but the clue book AND it is hidden too.

Any cheat maybe out there to get again to level 3?

I don't know anything about cheats. There is DOS-based trainer for EoB 2 where you could edit your characters' stats (including race and class) and inventory, yet I don't know the green hammer item ID #.

There is also a hex code for Walk through walls - yet again I have no idea how to activate it.
START.EXE
0001157D: 75 EB

I'm pretty sure (but not 100% sure) that you should be able to reach that particular location.
That said, there are a few game over moments for sure, where you can get yourself permanently stuck. But you generally know right away when this happens.

If all else fails, get All Seeing Eye, a nifty program that you can run next to the game in DOSBox, and one if its features is that you can give yourself items.

Edit: Loaded one of my old saves and yeah, you're absolutely right: You're not going back there through normal means.

I'm using the all-seeing-eye Software for automapping purposes. How do I add items with it? Didn't know, one can do it.

You right-click somewhere on the map and choose Character Editor or something similar.

That helped!!!! :-))))))))) Many thanks!

Is it possible to even teleport from one map to another?

Not directly I think, but you could teleport yourself to stairs on each level and walk up and down to get where you want to go.

I never used any All Seeing Eye features except for the mapping, but according to their website you can teleport anywhere.

Yes you can, but only on the level you're on. So you'd need to manually walk the stairs to another level in order to teleport around in there. You can't just teleport from the forest into the crimson tower, etc.
To my knowledge anyway. If there's a way to switch the map you're viewing, I'm not seeing it.

Yes, or course, teleport within the map. I just wanted to clear out the "not directly" part in your post, that's all.

I have read a lot about the Green Crystal Hammer being potentially inaccessible, causing players to be soft locked.

I have to debunk it here and now: This is not true. This was not helped by the game devs themselves: the reference card that came with the game plainly stating, you need to make sure to get it at the first opportunity (which IS good advice, don't get me wrong).

But that does not soft-lock your game.

The only truly inaccessible part of the Silver Tower after you complete it, is the final room with the 2 beholders and hand imprint pedestal.
The rest of the top floor can still be accessed:

Remember the 8 mouths before meeting Dran? Remember that only 7 of them were responsive and the 8th one was completely inactive in your first go around?
Go back and talk to it now that you have the mark of the moon on your hands. It will re-open the door that was shut by Dran. You can then pick up the green hammer at your leisure. No need for save editors, no need to restart a new game.
No need to lure a flying snake to it the first time.
The only way to permanenty lose access to the Green Crystal hammer is if you picked it up and then dumped it - on purpose - in the final room with the hand imprint pedestal.