Messy Riddle

[Flibert]

You can swim in me, you can walk on me!

What am I?

[GetOverIt]

Maybe - Seas ?

Seas on Earth and

The Lunar maria (singular: mare, IPA: /ˈmɑːreɪ/) are large, dark, basaltic plains on Earth's Moon, formed by ancient volcanic eruptions. They were dubbed maria, Latin for "seas", by early astronomers who mistook them for actual seas.

Although, only twelve men have walked on them !

[teddybon]

custard see john tickle brainiacs.

[tubeway]

Water - swim when liquid, walk when frozen

[weecalf]

Lane

[AniaSM]

Sunshine. You can sunbathe and be walkimg on sunshine.

[Salty]

A thixotropic liquid such as custard? If you walk fast enough you can walk across it before it envelops you, but at slow speed you would sink in. Whether you can then swim remains to be seen....

[Salty]

Sorry - missed teddybon's answer!