Carnivals are held all over the world. Some famous carnivals are held in Rio de Janeiro, Brazil, and in Trinidad & Tobago. Just to name some examples.
But you asked this question in the category "Germany". Here, carnivals are held all over the country. There are carnival parades everywhere. The biggest ones can be watched in Brunswick, Cologne and Mainz. Carnival time officially begins every year on November 11th at 11:11am and ends on Ash Wednesday. The highlight is Green Monday, the Monday before Ash Wednesday. It is a little different than in Rio or Trinidad & Tobago here. Carnival floats, which are shown during carnival parades, often have current political issues as a theme. People disguise as many different things; there are no rules for your disguise. I, for example, was a vampire last time. Carnival songs are sung and special dances like the ´Birdie Dance´ are danced. Carnival donuts are common carnival food here.
...In Rio de Janeiro.
The Rio carnival is the biggest holiday/party that is held in Rio de Janeiro in Brazil.
A famous carnival is held each year in Rio de Janeiro, this is the biggest and most famous carnival/party in not only Brazil, but almost the whole world!
Carnival in Rio De Janeiro is one major event in Brazil.
Rio de Janeiro
In Rio de Janeiro
Essentially all of Brazil is in Carnival from Lent until Easter every year. A few cities have spectacular events. Maybe the most famous is Rio Carnival in Rio de Janeiro
Rio de Janeiro, Brazil
Rio de Janeiro, Brazil.
The 2016 Olympics will be summer Olympics. They will be held in Rio de Janeiro in Brazil.
Rio de Janeiro, Brazil
Rio de Janeiro (in Brazil)
a carnival