The more of this there is, the less you see. What is it?

There are five vowels (a, e, i, o, u) in the English language.
Can you tell us a word that contains all these vowels?

I have a hole in my back and legs I lack.
I live where I can’t breathe and I eat without teeth.
What am I?

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?

The Puzzle: A girl, a boy, and a dog start walking down a road.

They start at the same time, from the same point, in the same direction.

The boy walks at 5 km/h, the girl at 6 km/h.

The dog runs from boy to girl and back again with a constant speed of 10 km/h. The dog does not slow down on the turn.
How far does the dog travel in 1 hour?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see?

I know a nine-letter word having only one vowel.
Do you ?

What has many keys but can’t open a single lock?

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?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.