I see some comments on fighting mold and smells, I have an experience devising my own protocol that was extremely successfull in my case.

Few years back I was desperate to find a large apartment in an area where they are just not available. I found one, extremely cheap, that the owner could not find anybody to rent to. The apartment was all but destroyed by previous occupants -- there was substantial mold in most rooms, heavy cigarette smell that was completely masked by even worse problem -- monkey pee and feces on every flat surface in the apartment.

Being geek I decided I will try what I can do and in the end I devised a protocol to treat the apartment. My girlfriend was very sceptical. A month later I brought her to apartment to the smell of fresh furniture and she was instantly converted. There was no fresh furniture, it was just the other smells were completely eradicated.

The only smell I could not get easily off and lingered for many months was banisters that were painted over with lacquer by the owner before I had the chance to treat them.

The treatment was:

1. industrial ozone generator (200 USD) + 200W fan + air dehumidifier (ozone decays quickly in humid air) + programmable timer and remotely controlled (over Internet) AC socket to control fan and generator (this let me turn the fan for 20 minutes every hour and let me turn everything off 3 hours in advance so I can visit safely without being subjected to high levels of ozone). This setup was on for an entire month except for when I was visiting to do other stuff in the flat.

2. 35% hydrogen peroxide mixed with baking soda. Ozone kills mold, binds and oxidises any smells except for urea crystals. To neutralize urea crystals you first have to dissolve them and treat while in dissolved state, before they crystalize again. I don't know what baking soda does, exactly (except for making cleanup tougher...) but I found dissolving some improves the treatment with hydrogen peroxide. I sprayed every surface (walls, floors, furniture, etc.) in the flat with this mixture enough to get it wet so that it dissolves and reacts with urea crystals.

Now, mandatory WARNING: both concentrated ozone and 35% hydrogen peroxide IS EXTREMELY DANGEROUS, you absolutely MUST spend time researching how to handle this stuff safely.

The hydrogen peroxide at that concentration INSTANTLY BURNS ANY ORGANIC MATTER IT IN CONTACT WITH. This includes your lungs and eyes if they come in contact with vapors or mist.

Concentrated ozone may also leave lasting effects on your eyes and lungs.

MAKE ABSOLUTELY SURE NOBODY ENTERS YOUR FLAT WHILE IT IS BEING TREATED, MAKE SURE OZONE IS NOT VENTING TO OTHER APARTMENTS, ETC.

One minuscule drop of 35% hydrogen peroxyde touched my finger and it felt as if I was shocked with electricity and the skin was instantly burned white. Don't even think about getting close to it without heavy nitrile gloves and face mask.

The fumes and mist will be extremely dangerous, I have used full face mask with external breathing aparatus to be on the safe side while I was spraying entire flat with it.

Test the effect on any surface before treatment and dilute with water until it becomes safe for that surface. I have destroyed some stuff at the kitchen where it reacted with plastic foil on otherwise metal oven exterior, etc. I ended up diluting it for everything except stained walls. For furniture I diluted it to around 5-6% hydrogen peroxide, for floor panels to around 9%.

ALSO, very important, 35% hydrogen peroxide naturally decomposes producing lots of hydrogen so if you store the containers for longer than few days you have to constantly monitor them and vent hydrogen before containers burst. Once you finish your treatment, get rid of it as quickly as possible -- it is a liability while you are storing it.

On the upside, and this was very important to me, this does not leave any lasting dangerous chemicals in your flat. Both the ozone and hydrogen peroxide decompose naturally into harmless products and baking soda is the only think you can really work to get rid of but only for cosmetic reasons -- so that your entire flat does not look as if it is covered in dust.