Before Mount Everest was discovered, what was the highest mountain in the world?

I look flat, but I am deep. Hidden realms I shelter. Lives I take, but the food I offer. At times I am beautiful. I can be calm, angry, and turbulent. I have no heart but offer pleasure as well as death. No man can own me, yet I encompass what all men must have. What am I?

How many letters are in the alphabet?

If you say my name, I will no longer exist. What am I?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

What has to be broken before you can use it?

Can you write down eight eights so that they add up to one thousand?

On her drawing table, Sayna lit 12 coloured candles. A few seconds later she blew two candles off.

How many candles Sayna have at the end?

What is the riddle which can be asked all day with a different correct answer each time.

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?