- [Mark] Almost a mile.

When you don't have a fear of heights,

it's not really scary.

It's like being in the craziest tree house

that you could possibly imagine.

- [Narrator] That's Mark Sinnett.

He's a professional rock climber,

and he's talking about sleeping in a tent.

- [Mark] They're called portaledges.

- [Narrator] That's hanging off the side of a mountain.

He's been climbing for over 30 years,

and his favorite walls to climb are really, really high.

- [Mark] Alpine big wall climbing is the pursuit

of scaling the biggest cliffs on planet earth.

- [Narrator] They take a few days to summit.

So he has to camp out along the way.

So I want to know what does it feel like

to sleep in a portaledge hanging off

the side of a mountain?

- [Mark] The one thing that's more or less ever present

in the mountains is when it can be pretty violent.

You can experience hurricane force winds,

there's also this thing that we call the Bronco ride.

Wind comes in, hits a cliff,

and it really has nowhere to go except for up.

Eventually it hits you and your ledge

and it can lift the whole thing off

so you can be suspended and then, of course,

the ledge like slams into the wall.

You're just thinking about surviving.

- [Narrator] And that wasn't the worst of it.

- [Mark] The smell in the ledge is not nice.

You don't change your clothes,

you don't bathe.

It's wet, it's gummy.

- [Narrator] But people love it.

They continue to climb and explore

through all of this punishment

because there's still that one question left:

How does it feel?

- [Mark] The way it makes you feel

is like a tiny speck of dust.

It's very empowering.

It really is just kind of like the most spectacular spot

that you can be on planet earth.

(peaceful music)