Cat won't stop yowling

I have 10 month Siamese who at the moment is indoors in a large home with lots of climbing areas, fed regularity and lots of toys. He spends his morning roaming in circles crying and his evenings when I get home from work doing the same. I have been slowly introducing him to the outdoors and I find the yowlingis worse after I do that. Personally I think he is desperate to be an outside Cat but I don't want to just open the door and let him roam while I'm at work. I took a video of his behaviour this morning but not sure if I can attach. Can health issues relate to this constant yowling. I know he is soamese but this is unbearable.

I have a Siamese mix who was house bound for much of the time from September to January. During that time my parents, who are retired and home 80% of the time, gave him attention on demand and played with him. I played with him when I got home. I got him a cat tree; that helped a lot. He would be after Rocket (my female pointed cat) every time she came in the house. Even with that he would cry every time we left him in the house alone (if we had dinner on the patio or were doing yard work for example). He would cry at night if doors were closed (although he does that normally) and if we left he room while he was asleep and he woke up alone. He knew my schedule and was waiting to tell me about his day when I got home. In the mornings he would want some play time and petting before I left for the day. 

Siamese are a very social, curious, and can be a high energy breed. They do not do well in homes where they are home alone for a long period of time. It sounds like your boy is alone while you are at work and is yowling for affection and attention before you leave and when you get home. I don't think the going outdoors has much to do with it (assuming leash training or supervised outdoor play) other than that is time you are spending with him, focused on him and he wants more. It could be he wants outdoor though for the curiosity and experience. I know Link loves to go outside but he adjusted to being indoors only while he had to with extra attention, interaction and cuddles. 

Ideally I would say to get a second cat so he isn't alone. Link and Rocket just would not be happy in a single cat household. Both just can't be only cats and there isn't a way around it. They both look too much towards each other for play and interaction and there is no way I could provide them 100% of that support they get from each other. Your boy may be the same but I realize that is sometimes not an option. It is double the food and medical costs but half the entertainment effort on humans. 

That aside when you say lots of toys, do you actually play with him or are the toys just out? If it is the later, he needs more interactive play with you engaged with him. If it is the former, try rotating which toys are out so he doesn't get bored. Take 3/4 the toys you have now and store them in an airtight container with some fresh catnip added in. In two weeks, put away the toys out and put out some fresh ones. Rotate every few weeks which toys are out. If he has a particular toy he likes more go ahead and leave it out all the time (my Link loves little fuzzy caterpillar toys so we have 4 of them scattered around the house with a few new ones tucked away as replacements). 

Thank you for the reply. I must say, my Linx favourite toy is his fuzzy catapillar too! How funny !