"Jdeme po pláži."

Translation: We are walking along the beach.

[Hatch-Slack]

Is the answer "We are walking on the beach." correct as well?

[endless_sleeper]

Yep.

[Hatch-Slack]

thank you!

[BrianSille2]

As BEACH, as I would envisage it does not exist in Czechia would this include a lake shore as, for example, at Lipno?

[AgnusOinas]

Good question. It would, nowadays: https://www.lipno.cz/volny-cas/koupani-a-vodni-sporty/plaze

Although a real "pláž" (sea beach) is still something Czechs have to travel abroad for, often to Croatia, there have been endevours to make certain lake/pond shores look beach-like and they can be called "pláž" in a broader sense. Originally, they weren't called pláž - that's why Czech doesn't even have a domestic word for "beach", as "pláž" is a French loanword.