My sims have a huge house with plenty open floor space everywhere, enough room for them to do even the most space consuming interactions and animations. All the same they insist on running outside to do almost every interaction, always picking the left corner towards the road, when looking out from inside.

Why is this? Is there a fix or tuning mod for it? It is absolutely ridiculous and rather takes away the point of having a nice roomy house to begin with.

Well, this is almost too obvious to mention, but do they have the "loves the outdoors" trait? Otherwise i think some combinations of objects, routing, and just quirky AI make them behave oddly.

I have a sim who for ages just walked out the front door to the sidewalk, summed her car, and drove away. I built a swimming pool in the back yard. Now she runs out the door, down the sidewalk to the carport, between the cars, through two fences (no gates), and halfway down the side yard, then turns around and runs back through the fences, between the cars to the sidewalk, and summons her car.

Also check which way tables and lamps face, this shouldn't make a difference to routing but apparently it does to the sims. I've flipped a coffee table so it faced the sofa and sims started using the area in front of it (dancing, conversation, etc.), where previously they just walked through there. And there are some ceiling light fixtures that hang low enough sims will not walk under them, so they can effectively block of an area of a room if not placed properly (if you cannot place a table under the light sims will not walk there either ...oddly you can place the table first then put the light over it).

Huh. Time to shuffle a few things around and see if it makes any difference, I suppose.

None of the residents love the outdoors. If they did, that would at least make sense. Ah, Sims 3, you are still the best game in the series to me, but you're far from perfect.

Path finding is weird in the Sims. In fact it seems to be one of those things that gives game programers trouble no matter how hard they work on it. Just look at any RTS where you try to have your army flank the enemy base and attack it at it's weak point only to have your units run through the strongest point of said base and only turn around to attack after half of your force has been lost getting to the weak point. I don't think we are ever going to see a 100% solution to this problem until computers get much more powerful and start "thinking" more like people.

On the bright side these mistakes can be very funny to watch. I once had a Sim who was cold from a snow storm and when he got inside he was then put in time out for bad grades, he then proceeded to strip down to his swim trunks and go outside to spend his time out standing in the pool, instead of standing by the lit fireplace he was at when he was given the time out. He then froze solid when it was over. I have seen AI programed in person and I have to say that no matter how hard you try problems are going to slip through so as long as it doesn't crash the game I just enjoy the sill things my Sims do that the programers most likely never intended for them to do. I see it as a fun bonus like finding a secret level in other games.

Poor AI path finding seems to be with us to stay but I say, enjoy it. It can lead to some fun moments.