That's a great question

What would you do? That's a great question.

'That's a great question' means that someone has asked something that is interesting.

Notice the following:

1. Thank you for asking that, that's a great question.
2. That's a great question; I think I will find out.

tons of people

Mount Royal is a big mountain in the middle of the city where tons of people come.

'Tons of people' means the same thing as 'a lot of people' or 'many people.'

Notice the following:

1. I have invited tons of people to my party.
2. There are going to be tons of people at the festival at the weekend.

a big drum circle

People from all over Montreal have drums and do a big drum circle.

A 'big drum circle' is when groups pf people stand in a ring and beat drums in time with each other. This is a very common activity with hippies.

Notice the following:

1. When I went on holiday, I took part in a big drum circle with my friends.
2. There was a big drum circle, it was great fun.

flea market

It's turned into a bit of a flea market; you can bring the family.

A 'flea market' is a market that sells second hand, vintage items and unusual things.

Notice the following:

1. I love to wander around flea markets and try to hunt down bargains. 
2. I am going to try and organize a flea market and raise money for charity.

strolling around

You just finish off your day strolling around Prince Arthur Street where they have clowns and outdoor comedians.

When you 'stroll around' somewhere, it means that you wander slowly without being in a rush.

Notice the following:

1. I like to stroll around the fields with the dogs.
2. I bumped into them in the city; they were just strolling around.