The cantrip Mold earth allows
"shapes, colors, or both to appear on the dirt or stone, spelling out words, creating images, or shaping patterns"
Could those shapes be a series of ledges and/or indentations to make a ladder for climbing out of a pit or up a stone wall? The degree to which those letters/patterns have depth isn’t specified.
The steps would disappear after 1 hr., and only two ‘areas’ of such steps could exist, but within those limits ascent could be via a series of castings of this spell:
- Cast and climb as high as possible on that first section.
- Cast again above the first area and climb as high a possible on it.
Presumably, one would ascend at at rate of 5′ per round this way: the excavation use of mold earth specifies a 5′ cube. There is no specification of the area that can be affected by a shaping use of this spell, but 5′ x 5′ seems reasonable and consistent with that 5′ cube.
The higher level spell stone shape allows more sophisticated, and durable manipulation of stone: as a weapon or coffer, and possibly with 2 hinges and a latch. Would using mold earth to create steps steal the thunder from stone shape? I would argue that the 1 hr. duration and limits on 2 ‘areas’ (however big those might be), and the implied limit that mold earth can only work–literally–superficially (as the "shaping patterns" suggests), could be sufficient to keep this use of the cantrip from being overpowered.
However, another objection might be that the spell as written specifies creating shapes, patterns, colors, and letters suggests manipulations of the stone that are visually detectable–I could see those at more in line with creating a sign is viewable, or readable like braille, but not climbable. That is a harder argument to rebut.