Don't know what to do at the gym tonight

My suggestion:

Start a lifting program. If you need suggestions NROLFW is good, Jamie Eason has a good program, stronglifts 5x5 is pretty hardcore too.

Depending on how you feel, either just do that if you're beat, light cardio if you're tired but not done, or HIIT if you have a lot left in the tank.

Get on a treadmill and do "Sprint 8" . It's easier than it sounds, as you control the speeds. It's 8, 30 second "bursts" followed by slow rest periods. I find it fun. You can change the burst speeds from all out Sprint to a brisk walking pace, takes about 20 minutes and is something to do :-)

That's what I was thinking molson622. I can't be on any machine too long without getting bored as hell so I thought I would mix it up with 10 - 15 mins on each one until I felt tired. Then move on to some weights for a few.

Do the weights first, however you choose to lift the muscles you target should be beat when you're done. It's better to do cardio (unless it's as a warmup) after.

I run into this same issue on some nights when there are no Body Pump classes and I have to hit my backup gym for a free-form workout. What I do sometimes is try and do my own Body Pump class. Take a small piece of paper or a note card and write down as many of the Body Pump exercises that you can remember. If you are new enough so that you don't remember much yet from the classes, YouTube can be a great resource for Les Mills videos and routines.

Get your MP3 player and cue up a bunch of 3-4 minutes dance tracks and then get to it! I have found that I don't have to remember all the counts and specific combos for each exercise but just keep your weight at your level and do your own custom combo of singles, 2 up/2 down, 4 up/4 down etc. Just like in class, focus on low weights and many reps and just keep moving. Even if you only get 1/2 of the usual workout you get in class you can combine this with any of the previously suggested workouts and you will definitely get your exercise in. Good luck!