The first show of Doomsday Bunkers on National Geographic was a great start to the topic of living in an underground bunkers. It was fairly obvious that all of the bunkers were quite expensive but also of excellent quality which might very well save your life one day, but is it the right choice?
With so many options for underground Shelters or bunkers it may take a bit of forethought to decide on a solution that works well for you. Storm Shelters have been built for years in Tornado Alley and have withstood much of the forces mother nature could throw at you. If you are considering the possibility of a pole shift those forces will most likely be much more extreme and of a longer duration. One of the key features of any bunker would be its ability to withstand such forces. Many survival shelters build for protection against tornado's are a cement block structure. These are very good when protecting from high winds in an earthquake scenario it would not hold up as well as a bunker made of steel and reinforced with ribs.
So with that said what are you looking for in a bunker? If it's for a short duration say a couple of days then you have many more options available to you and do not have to spend time considering power, sewage, water, filtered air etc. You could probably do fine with a much smaller stockpile also. If on the other hand you are looking at maybe being underground for 3 months or longer you'll need to put a lot more planning into your survival bunker to make sure you have plenty of water, air filtration, sewage treatment or at least a way to get rid of it as well as plenty of room for survival rations.
Another aspect to consider if you were to live in an underground bunker is the mental aspect of it. Think of a family of four in a bunker of say 600 sq feet. It's doable but 4 people in that little space without access to the outside is likely to take a toll on everyone mentally. There are quite a few ways to help that. One thing that has proven to help underground is higher ceilings so you might consider making 10 foot ceilings. Also the colors inside should be bright and reflective so that any light source is amplified to help you feel less like you are underground. Things like pictures of your favorite place might also help you feel like the real world is right outside the window.
Then there is the physical to consider in a bunker. Working out would probably be essential to keep your condition up and help alleviate the stresses of living underground. You'd also be lacking in Vitamin D which is already a problem for people who live in really rainy areas due to lack of access to sunlight. I'd recommend getting a supply of vitamin D and taking at least 2000 to 4000 units a day (usually 2 pills). This will help as when you get a low vitamin D you get lethargic, start to feel depression and a range of other issues that will make enduring for 3 months underground much harder.
Consider also having activities to do, games, books, movies and the like. If you have access to power you could have a lot of movies on DVD or a hard drive. A kindle book reader is also a good choice as you could have lots of books on there and take up much less space in your bunker than having room for 100 books.
You should also make everyone responsible for some chores on a daily basis so everyone has something to do, you might not be able to keep them busy for 8 hours but at least knowing there are expectations of what you need to do on a daily basis is a good way to keep depression and anger at bay.
Lastly if you are going to get an underground bunker, give it a try. Do not wait until you have to use it to find out you are missing something or need to overcome the physical and mental drain of living in an underground doomsday bunker. Spend a couple of weekends up there or even a week. Be prepared and stay alive. That's what Doomsday Prepping is all about!