I recently ran a full marathon and would like to set a new goal for myself. I'm not looking to compete, just challenge myself physically. I'm deciding between a half ironman or triathalon. What would be challenging but not too difficult for a beginner. Any advice would be greatly appreciated!
So a half ironman is a triathlon (swim, bike, run) it is just a certain brand called ironman. You may see some non-ironman triathlons refer to the distance as half iron distance which is a 1.2 mile swim, 56 mile bike, and 13.1 mile run.
Triathlon distances are usually (from shortest to longest) super sprint, sprint, olympic, half iron distance, and full iron distance.
I would recommend looking for a sprint distance to find out if you want to stick with the sport.
A sprint is usually around 1/4 mile swim, 12-15 mile bike, and 5k run. You can complete this distance without any fancy triathlon gear (it can get REALLY expensive). All you need is a swimsuit, a bike, a helmet, and some running gear. You can also do a sprint on pretty minimal training and figure out if you will enjoy the sport or not. If you decide you would enjoy the sport, then I would look at some olympic or half iron distance triathlons around where you live and plan out for them.
I'm doing my first half ironman next Sunday after coming from a running background and completing a sprint in July. I have enjoyed the break from running specific training but have also been irritated at times with the swimming and biking aspect in terms of cost and logistics. It's hard to find a good place to swim or ride near my home. With biking, there are so many things that can go wrong and ruin a workout whereas with running, you lace up your shoes and hit the road. No worries about flat tires, dropping chains, pool times and all that.
Good luck and I hope you enjoy the sport. I think it has made me a more well-rounded athlete.
I would start with a shorter distance like sprint or super-sprint, UNLESS you have a strong swim background (i.e. you could go out right now and confidently swim 2 km in open water with or without a wetsuit). If you have done a marathon, the run in a HIM doesn't feel any worse than the back half of that, normally. And I think it would be pretty doable for someone with good endurance to build up to biking 56 miles by spring--maybe not fast, but enough to complete the race distance with something left for the run. (This assumes you can either bike outside in the winter or are willing to spend time on a gym spin bike or invest in a bike trainer to bike indoors.) If that's not the case, a sprint tri would be a realistic beginner goal, maybe Olympic distance if you swim background is a bit stronger and you can work on the swim regularly.
The swim would be the limiter--cannot stress it enough. You need to be confident at completing the race distance (not necessarily fast, but within reasonable time limits) and then some, in potentially rough conditions in open water (unless I guess it's a pool swim tri--some early season sprints are), with a bunch of other people who might slap, kick, and swim over you. If that's not true, it doesn't matter how good a biker or runner you are, you're not ready.
If you're in reasonable shape, and if you did a marathon I think you are, and aren't one to obsess over your time then I would go for Olympic distance. It is essentially a quarter iron man (roughly). The sprints I find annoyingly short, it feels like you spend most of your time changing clothes in transition, but that may just be me. I don't even think you need worry too much about the swim, from a speed standpoint, so long as you don't have any concerns about open water. I spent plenty of time on the water growing up so it doesn't do anything to me but some people really get concerned about it. I was 35 or so at my first Olympic, which was my first triathlon. I had been a runner only before. I did the swim in a regular bathing suit and the bike on an old rented piece of crud from the back of the bike shop (I only owned an old super heavy mountain bike). And lest ye think I am a super athlete I have the body type of one of those guys who puts the comically large top hats over their upper body and then draws a face on their gut and dances around. I finished near the bottom of course, but I'm glad I did that distance.