The Coliseum

The coliseum takes up an entire district, and from a birds eye view it appears to be honeycombed of sorts - with a series of smaller arenas throughout it. There are 3 types of events to witness or take part in. "The Arena", where people face off against people - until submission or death. "The Crucible" - where combatants fight off waves of hostile creatures, and are paid for each round they survive. "The Sanctum" - a large arena built in the center of the coliseum hosts the main event - a team of fighters face down a legendary creature for a hefty sum of gold and platinum.
The Arena
There is no limit to how many people you wish to fight by your side, but this will also determine how many people you will be facing. Each person is paid 25 gp per level of their character upon victory. The fight does not need to end in death, but rather simple submission or knocking your opponent unconscious will suffice.
The Crucible
The combatants face off against a creature of 1/4 cr of the parties level, and each round they prevail and choose to continue - are greeted with a fight involving one more of these creatures than before. The initial gp amount paid for the first round is "5 gp x the parties level" - and for each round won after the first one, the payment is doubled.
The Sanctum
As a meta rule this particular event can only be done once per session, as the creature - and the always changing terrain of this section of the coliseum is something that must be prepared before hand. The combatants who choose this challenge will face a creature of legendary origin - and meta-wise, this fight will always be considered "deadly". Payment for successfully vanquishing the creature is 250 gp per level of the party - as a lump sum.