Money can be exchanged in most hotels (at a lower rate than the banks usually) or in most of the city's largest banks, custered around the Matuna or inside the walled city close to the Clock Tower.
In Calle del Badillo and Calle de las Carretas there are also a concentration of money exchange places, which give good rates.
It pays to research the exchange rate before visiting any of these places and if you are planning on changing a large sum (more than $1,000.00) you can often haggle on the rate.
See a quick guide to the rate today here.
Rip off merchants
Whatever you do avoid the shysters lingering on the edge of the walled city - the ones that will offer you a rate 200 pesos above the market rate and then leave you wondering how they short-changed you.
It's all in the fingers and the folding over of a few bills so they are counted twice. Either that or they will leave you with a handful of fake notes. Avoid them like the plague.
If you need to receive a transfer from abroad then supermarket chains Olimpica, Exito, Homecenter and SAO have branches of Acciones & Valores, the agent for Western Unionin Colombia that charge a percentage on money sent and / or received.
In terms of spending your holiday funds a 10% tip is normally included in the price of any bill in restaurants and bars but feel free to leave more as it is more likely to make it into the hands of the person serving you.
Haggling in the shops is expected and Colombians pride themselves on their negotiating skills. Over-charging gringos is a popular sport so be prepared to give as good as you get.
Throwing money to poor kids on the street isn't encouraged as it tends to fuel a drug habit. If your conscience is weighing you down it is better to buy them something to eat and drink than to give them money.
If you really want to help the lives of the Colombians then its probably better to tip heavily or contribute to one of the many Non-Government Organisations in Cartagena de Indias trying to make a lasting difference. Click here to see more about volunteering or charitable donations.