As he steps out onto the marbled surface, a shoesized area reaches up to meet his foot. Each step raises to exactly the same level, creating the illusion of a perfectly flat floor that only appears when he's about to step on it. If he stumbles, the floor changes to lessen the stumble.

The imposing airlock door hinges outward, attached to the top of the door. It's designed to be opened manually, so there is a counterbalancing mechanism that he's likely seen a schematic of in passing during his studies. This means he just has to move the mass, and not also hold its weight up against the slightly higher than earth gravity the entire time, which should make this entirely doable.

Well, if he could get started. While the mechanism seems fine, the early part of the descent, before the hull ruptured and could equalize the pressure inside and outside, put a lot of pressure on this door. This wedged it in place, misshaping the edges.

As he pulls the lever, he can hear a seal open and air rush into the airlock, but he doesn't manage to move the door at all.  The floor near the bottom of the door ripples in response to his actions. Does he keep straining?

He considers trying something elaborate. But first: MORE BRUTE STRENGTH.

He puts all his weight on pulling the door. Does it bulge?

Yeah, no, he's not moving this on his own, at least not like this.

As he keeps pulling, two bulges in the floor appear under the door off to the side, vaguely spaced like his hands.

Oh, yeah, the membrane thing.

"Uuuuh. Can you hear me?" This is silly, but. "Can you help me open this door?"

There is no response, at least no words. But the motion of the membrane stills when it is addressed, and then a couple moments pass where nothing happens, followed by a rippling near where he was standing.

Slowly, a pair of appendages grow out of the ground, and the tips form into what you would get if you draped a cast of Mark's hands with an extra layer of marbled skin. The arms tentatively mimic the motion you would get if you just looked at Mark's arms when he was straining, but seemingly without applying any force at all to the lever.

Welp. That is less than fully helpful.

Can he get to any other airlock while staying inside The Membrane?

The space he finds himself in is a tube that connects a tight fitting shell around the spaceship to a seal around the pod. He can walk around a bit in any direction but it's not much larger than required to connect the vehicle size airlock to the pod.

If he wants to go to another side of the ship, the only real chance would be by squeezing himself between the Membrane and the ship for perhaps a fairly long distance. Maybe?

When the membrane sees him not be satisfied with its action, it morphs and imitates his current thinking stance with an amorphous blob. And then the walk from the pod to the air lock. Then it hesitates. It does not at all seem incorporeal. 

Ok, so, it imitates him. But when it imitated him pulling the lever it didn't apply enough force.

It did sustain him while he was walking, so it can definitely apply at least 70 kilograms of force, and do that in a precise way even.

He tries to touch it, trying to imagine how it would feel to squeeze between the membrane and the spaceship to get to the next airlock.

The membrane reaches out a bump to make itself available to be touched when he reaches out. It feels hard and like it has many interlocking pieces, behind a softer surface. Roughly the same as when touching the back of his own hand, with bones and cartilage behind a layer of skin.

It is, of course, still humid, but it seems like it has been drying over time.

If he holds his hand to it for a longer moment, he can feel the subsurface parts slowly rearrange. It seems like it's being careful not to pinch him.

If he applies some force with his palm, he can not deform the hard parts at all. They seem very strong. The soft surface layer squishes though.

This is going to suuuuuuuuuuuuuuuuuuuuuck.

He tries to squeeze between the membrane and the spaceship to get to the next access point.

As he nears the intersection of membrane and ship, the membrane first reaches out to allow itself to be touched again. When Mark then walks around the bump, and starts trying to squeeze through, the membrane starts to adjust to give him more space. It's slow though, so the first few meters are icky close contact moments where the moisture of the membrane and the ship ends up on the vacuum suit. Then it starts opening up to a shuffling area. Then a walking area. It caps out somewhere about a meter away from the ship, which is not roomy but enough to get around without touching either surface.

The ship is not that large in walking distance terms, so he doesn't have to walk that far to find the next interesting part - a huge gash in the side of the ship, where the hull ruptured on the way down. The entrance has loads of pointy metal pieces, all pointing inward from the water pressure, but there are some nasty sharp edges on all sides. The surfaces that are not sharp look slippery from moisture.

Behind the gash is an atmospheric turbine engine, mounted on a structure that holds it slightly away from the hull. Its shape indicates that this is port side of the ship. The engine seems in fairly good shape compared to anything that would have held pressure for a while.

The membrane here has patches of something that looks slightly different. It's slimy and with a vaguely orange color. The shape of the membrane's blue part tend toward shapes that hinder him from touching the orange bit, with barriers extending as far as it can, and contracting around it, decreasing the surface area. If he reaches for it, bits of blue try to intercept his hand and gently push him away, although slowly enough that he could win a contest of speed.

The membrane keeps the start of both the direction he was walking and the reverse open for him, but the areas farther away from him has returned to their previous shapes of very tight squeeze width.

Uuuuugh. Wait, no, ok, that's better.

He tries to touch the orange thing, but when the membrane intercepts it he gets the hint and doesn't try his luck. If the membrane decides it doesn't want to hold the pressure anymore it would get pretty ugly pretty fast.

This is a possible entry point, but it seems kinda dangerous. While the membrane is collaborating and not promising more moist contact he'll try to walk around and find other possibilities.

The membrane seems to relax slightly when he stops trying to go for the orange part, similar to how the skin of a cat moves over its muscle.

The membrane keeps making way for him, but seems to need to shift macroscopically to allow him access to the other side of the ship, so at some points, the opening increases to walkable slowly enough that he has to stop and wait. During those moments he can sometimes feel the vibrations of something huge shifting across a surface.

As he ducks past the turbine and walks around the back, he walks past a part of the vacuum propulsion engines. The massive cylinders are too large to fit inside his human-height walkway, so what he sees is just the horizontal slice at this height. The engine exhausts are very wrecked. Something inside imploded at some point and took part of the exhausts with them. 

Around the back, now on the starboard side, he walks past a similar turbine engine, but it seems like he's farther up now, such that he needs to walk around or over it. Thinking back, he has been walking at a slight incline. This turbine is pivoted slightly differently, as if to boost upwards slightly.

The next thing he sees is a human sized door which says "turbine maintenance room access". The ground seems to level out at a very good height to interact with it, despite being quite a lot higher on the ship body. The door has an emergency lever similar to the other one, but in a much smaller scale.

That's... not a great sign for how he'll find the rest of the ship. Still beats slowly asphyxiating in the escape pod...

Time to puuuuuuuuuuuull the emergency lever!