Now, this is going to be a hard task, so you will all forgive me if I get a bit confusing or I'm not properly clear.
Chapter Art Centre is a big building in one of the main areas of Cardiff, Canton; and let me please dwell in a little digression in this regard. Canton is a rather peculiar area of the city of Cardiff. I have to admit, the first time I had the chance to go there I honestly didn't like it. It's a bit rough, and on the surface it might look fairly suburban. One has to go there various times to fully understand it and enjoy it. It will appear, in the end, as a small town by itself, inside a bigger city, with its small markets, the good grocery shops and the small places only usual customers know about.
It is in this least extraordinary environment that you can find Chapter. If you ever want to spend the afternoon outside, to do something without walking around in the cold (aka spend the afternoon opening and closing the umbrella, finally having to throw it away as the wind has broken it, then going home and spend the next three days in bed as you obviously caught a terrible flu), this is your place. In Chapter, you can basically do everything: you can eat (and I assure you that food here is very good! Strongly recommended! ), you can listen to live music, you can watch a film (choosing from a widest variety of films of any kind); you have the possibility to attend a performance or to visit the art exhibition. It's basically the most complete centre you can find: if you don't know what to do but you don't want to waste your whole evening watching TV series online, go to Chapter, you will most definitely find something to do.
For what concerns more useful information, I have the duty to recommend you, in the area of food, the sweet potatoes fries with garlic mayonnaise. Heavenly. They made even the pointless night out worthy. Of course, consider the cons of eating fries and garlic: speaking from experience, don't order them if you are going to have a romantic evening.
The Art Car Bootique. Last year in May (Sunday 25th May), two friends and I went to the nicest of the events, organised in Chapter: the Art Car Bootique. It's a fair, established in 2011 and still happily surviving. We had awesome food, drank beer (as last year it coincided with Maibock, the annual springtime German ale festival), attended free art and music performances, all sitting on the ground in front of a stage, with children dancing and people of all ages drinking and chatting; we bought vintage clothes, enjoyed funny performances, made nice prints with flowers and played any kind of game (such as, throwing tennis balls to politicians, as in the picture below. It was delightful seeing Berlusconi's face at this stand! ).
My friend trying to make some music out of a very original and new-age instrument.
So, moral of the story: go on Chapter website, keep up to date and attend every event organised in Chapter. I assure you, you won't regret it!