I have found an very old post with regards to this.
I propose to use the MuTeRe effect. I think turning earth into air is not a good plan, first you'll get choked by your own parma if it doesn't pen and if it does pen you'll have lungs full of dirt if the spell ends before you get allot of fresh air before the spell ends.
I plan on using the Re effect to reinforce the dirt around the caster into a dome and the Mu to shrink the contents inside the dome and turn it into gravel.
My best guess looks something like this.
Wondering Cave.
MuTe(Re)
Lets a mage sink into the ground while reinforcing the walls of the pit being created until he is fully submerged in the earth the pit closes to a 2 paces wide and 2 paces tall cavern. The interior is walled in dirt and stone packed hard enough to be as stone. While the spell is active the caster can push in any direction to "move" the cavern in that direction.
This is done by changing the contents of the pit into gravel and shrinking it until it is moved out of the spell's range where it fills in the previously occupied space.
Base 4 +1 touch +1 Req +1 Conc +1 effect stone +1 part.
Yes and no. Procedurally, it makes sense. Magically, lungs of the fish doesn't make you spit water at the end of the spell. You also don't need to penetrate your own parma magicka - you could willingly let the spell affect you.
A couple of feedback:
Base guideline 4, +1 requisite, +1 touch, +1 effect stone seems appropriate;
Concentration will indeed let you vary the direction you're traveling;
You are missing target part, since you're affecting the ground;
You probably should include a description of the speed the magi is traveling at, and appropriate finesse rolls to vary the direction and speed, if appropriate. Walking speed doesn't warrant a finesse rolls, but 30 MPH definitely would;
You're missing a max distance traveled and a size parameter. Bear in mind that you need to affect not just the size of rock arround the magi casting this, but all the stone that the "capsule" is traveling through, since stone doesn't naturally allow stone to travel through it.
A base individual of Terram is a cubic pace, which translates to 27 cubic foot. Lets imagine a 1'6" by 3 foot by 6'8" capsule. This is a base individual of stone, large enough to fit a magi and not make him feel too constrained. If you're going by the shrinking approach, you can collapse that area by 7/8th of its volume without adding magnitudes. This leaves 15 inch x 2'7" x 5'10" for the magi, the rest being the shell (claustrophobic or tall magi should abstain). Now, you must account for distance traveled. Every size magnitude multiplies the volume of stone affected by 10. So with +1 size, you're looking at traveling 66 feet, 660 feet with +2 size, etc. You're looking at +3 size to travel for roughly 1 km and back to the surface, +4 size would let you thoroughly swim through a big mountain and at this point, since we're talking about roughly 20 km of swimming distance, speed will really matter and finesse becomes a must.
So the final effect we're looking at to let you swim through a mountain looks like this:
Mu(Re)Te 45 + finesse check
Base 4, +1 rego requisite, +1 touch, +1 part, +1 concentration, +1 effect stone, +4 size
And should you encounter a metal/gem vein on the way through, you would be stopped, which could plausibly result in a wound for crashing at 30 mph if you haven't thought of a protective helmet Arguably, adding an intellego requisite and an extra magnitude could let you instinctively avoid those, and the final level would be 50. Or a higher difficulty Finesse roll when encountering metal/gem to stop smoothly.
If you don't need to actually cross a mountain, and you're just looking at re-emerging above ground some 600 feet later, it's a much smaller effect - Mu(Re)Te 35... but still more prohibitive than an equivalent R: Per Rego Corpus effect if you have line of sight / an arcane connection to your destination.
Moving through earth, and not stone, would be comparatively much easier because you're both skipping the magnitude for stone, and affecting a way larger volume of material for less magnitude at the same time. Mu(Re) 25 would give you a travel distance on plains of 200 paces vs a ReCo 20 effect where you travel 500 paces anywhere you can see, and require some time traveling.
So what is in the pit is the only air the caster can breathe, right?
The typical spell to merge into the earth is ArM5 p.132 The Silent Vigil. But it does prevent most senses and penalizes spellcasting seriously. Adding a Rego requisite to it might allow the caster to move - but orientation is still a problem.
That spell has a sun duration, so I'm guessing that you have some time to breath normal air below it ends.
Yes, that's what I was forgetting!! Thanks, I'll do an edit and add that.
It is in fact 10 cubic paces for dirt clay and mud, I added the +1 effect stone so the spell can handle up to a pace worth of stone?
The cavern is is a 2 pace wide circle that is 2 paces tall, that's just over 6 square paces, the rest is filled with the shrunken gravel.
The spell was intended to be used for short walks into the earth about 2min of air in the space with you, you can surface to get some fresh air or use chamber of spring breezes for longer periods of travel.
I have no idea what you mean with this.
You cast the spell and the ground swallows you into the "cavern" if the spell is still active you can turn in the direction you want and press on the shell/wall you can lift it to walk up hill and press down to walk down hill and the entire chamber moves by transforming the dirt and stones into gravel and shrinking it for you to walk on, then when it get to the far end of the chamber and turns back into what it was before the gravel and shrinking took place.
How good you are at concentrating while walking is the only limit to your distance there is no propulsion affect... and air.
Hmmm, I may not be explaining this very well. Lets step through this in a more illustrated fashion.
A mage casts this spell. The ground under his/her feet turns to gravel and seems to compact (Shrink) lowering the mage into a pit. At 2 paces deep the pit closes over the mage. He/She is now standing in a cylinder shaped space 2 paces wide and high.
The focal point of the spell/cavern is on the mage's hand, he/she moves forward extending his/her hand and the wall before him/her cascades to the ground as gravel while the gravel behind him/her forms a new layer of wall behind him/her.
The mage encounters a vein of ore as parts of the wall before him/her fall to the ground in a large clump rather than the gravel that is normal for this spell, the mage may choose to step over or around it or collect it if they so desire and continue.
By moving the focal point up or down the cylinder new cascade for gravel slopes up or down thus bringing the chamber closer to the surface or deeper into the earth.
Arguably, adding an intellego requisite and an extra magnitude could let you instinctively avoid those, and the final level would be 50. Or a higher difficulty Finesse roll when encountering metal/gem to stop smoothly.