Amran: I slipped together a mod which re-implements the ten missing levels into Rune Classic, this post contains download and installation instructions. Rune can certainly be a bit of a grind when played at full length (which I suspect is why these were dropped from the Classic release) but it seemed like it would be nice to have the option for them to be included in the campaign once more.

Download - Rune Classic Extended

I'd recommend making a backup of the maps folder before replacing any files in case you want to revert later without re-downloading the game. Also take note that loading a save game from a map which has since been replaced may cause issues in some cases.

To install, first remove the suffix '_CUT' from any levels within the ..\Rune Classic\Maps directory. There should be ten of them as listed below. (Example, 'DeepUnder4_CUT' should be changed to 'DeepUnder4', and so forth)

DeepUnder1OdinB_CUT -Becomes-> DeepUnder1OdinB
DeepUnder4_CUT --------------------> DeepUnder4
DwarfMap5A_CUT --------------------> DwarfMap5A
DwarfMap3A_CUT --------------------> DwarfMap3A
DwarfMap3B_CUT --------------------> DwarfMap3B
Goblin1_CUT ---------------------------> Goblin1
Hel3b_CUT -----------------------------> Hel3b
Hell2End_CUT -------------------------> Hell2End
Mountain1_CUT -----------------------> Mountain1
ThorMap4B_CUT ----------------------> ThorMap4B

Now, copy the 11 map files from the archive into the folder, replacing the originals in the process. You're now ready to play!

Here's a list of what was modified in each level. 'Changed transition' refers to changing the next map to be loaded, while 'restored geometry' means I brought over content from Runes original levels so the transitions line up as they do in 1.07 and below. As a long time fan, I made absolutely certain to be faithful both to the original game, and to the gameplay changes made in 1.10.

DeepUnder1Odin <-Changed transition, restored exit geometry.
DeepUnder3 <-Changed transition, restored entry geometry.
Hel1 <-Restored entry geometry.
Hel1b <-Changed transition.
Hel3a <-Changed transition, restored entry geometry.
HelLift <-Changed transition, restored entry geometry.
Goblin1 <-Added 1.10 entry geometry.
Goblin2 <-Restored entry geometry.
ThorMap4A <-Changed transition, restored exit geometry.
THORmap6Loki <-Changed transition, restored exit geometry.
DwarfMap2 <-Changed transition, restored exit geometry.

Spaceman71: On the map "Hel3b.run" the game freezes when the zombie breaks out of the wooden wall. You can only continue with the "ghost" cheat. If you break the wooden walls yourself, the same happens. This mod needs to be fixed.

Citronvand: Yep, just happened to me as well.

EDIT: Seems to be a problem with the audio. If you disable the sound in-game you can prevent the crashes when destroying the wooden walls. You can easily do this by simply going into options and drag the sound volume slider all the way to the left.

arondash: Thanks. I had the same bug and muting the sound from game options did the trick.

waltc: I'm actually playing classic now under win 10 and my current AMD 380 4GB drivers, Crimson ReLive 16.12.2's under Win10x64, build 14986.1001 are running great! Wooden walls, smashing through, no problem...;)

I also discovered that the GOG version I have already has all of the "extended" Maps installed--just have to open the Maps directory and remove the "_cut" letters and you are there. Also, the files linked in this thread are dated 2012--the GOG Map files are all dated 2013--but that may not mean anything...;) The files I got from this link do not use the _CUT designation but are already properly named and can be directly copied into the Maps folder the way they are--if you don't already have these files. Anyway, was surprised to see these files already in my Maps folder.