Blue Lagoon can be an amazing once in a lifetime experience because,
- Service: The only good thing is that the entrance ticket gets you also a facial mud mask, a towel, a locker, free toiletries (shower gel, shampoo, conditioner) and a free drink in the pool. So it is a fact that you have to pay a lot of money, but you actually get to chill out and enjoy your time like in a luxurious SPA. The staff are nice and they actually have one of the best conditioners I have used in my entire life - I have curly and dry hair, so you do the math.
- Temperature: Since this is not a natural pool, but is controlled by people, the temperature of the water is constantly around 40 degrees Celsius. When we were there, it was rainy and cold August day and we never felt the coldness that is outside, since the water itself is really warm. Plus, the foggy weather gave us an amazing view and we were kinda happy to get a more misty look. So do not get disappointed by the weather or the temperature conditions.
- Indoor facilities: Even in August, we had wild weather conditions. It is true that there are free pools everywhere and you can take advantage of alternative natural options, changing your clothes and tying to get dry once you are out from the pool would be problematic - especially if you are not lucky with the weather. Blue Lagoon offering you everything - shower, lockers, towels and hair dryer makes everything much easier to pack and get back exploring once finished.
- View: I travel quite often and let me tell you this: Blue Lagoon is one of the only places where the actual view is exactly the same as in the advertisements. No, really. The water is REALLY that blue and the experience is REALLY that relaxing. I cannot tell you if you will enjoy it or not, but I can tell you that you will not be disappointed. I mean, look at this!
So, if you decided to go, here are a few points you might be wondering about:
BOOKING
July and August are claimed to be high season for Iceland and this time is especially important to book your reservation in advance. You simply need to check the official website
https://www.bluelagoon.com, choose the suitable day and time slot for you and make the payment online. You will automatically receive an e-mail with your QR code, which you will use at the ticket office. I have purchased a month before and there were some time slots that were already fully booked, so if you have a strict plan, act early.

WHAT TO BRING
QR Code of your reservation: It is up to you to bring along a printed out version of your reservation proof or to use the electronic one from your phone. Just make sure that you have it somewhere.
Swimwear: Be aware that the water of Blue Lagoon might actually be bad for your bathing suit, so if you have an old pair that you can spare after your Iceland trip, I would suggest you to stick to that one.
Flip flops: You might need it for the shower or to reach the lakeside.
Hair Band/Tie: The water of Blue Lagoon is stated to dry out the hair so much that it doesn't wash off in a week. Well, personally I didn't experience it because after reading this warning, I decided to keep my hair off the lagoon.
Shower cap: Before and after the lagoon, you are asked to have a shower and having a shower cap might save you from some trouble if you decided to keep your hair dry like me.
Towel: You are given a towel for the lagoon, but you might be glad to have an extra one for after shower.
Camera gears: You are allowed to bring your camera in the lagoon with you. Bring along your stick if you need. Keep in mind that you cannot shoot under water photos, but bring along your waterproof protection against the steam and drops.

WHAT NOT TO BRING
Googles: Blue Lagoon isn't a swimming pool, it's a SPA. All your swimming equipments will be irrelevant here.
Sea shoes: This is up to you, but keep in mind that the bottom of the lagoon is safe and smooth and the water is anti-bacterial by definition. So, you won't need them, but you can bring if you want.
Lock: Your electronic bracelet opens and closes the automatic lockers in the changing rooms. You won't need them.
Hair Dryer: Again, unless you need your machine for some reasons, you can simply use the machines in the changing rooms with no charge.
Your Luggage: Not to cause a caos in the changing rooms, the visitors are not allowed to bring their big bags or luggage, but they can use the storing room in the parking lot if you need.

ENTRANCE
There are two things you have to pay attention about entering the lagoon: you have to have your QR code with you and you have to present at the time slot you purchased. If you booked to enter at 9.00 AM, you can enter between 9.00 - 9.59 AM and your booking might become invalid if you are late. Depending on the workload, you might still enter for early or late showing up, but I wouldn't count on it.

At the entrance, they give you an electronic bracelet to open/close a locker for your personal belongings and to get your free drink or purchase other items at the bar. In case you make some purchases, you should claim these expenses and make the payment accordingly. Keep in mind that once you enter the lagoon, you cannot go out again. You can stay in as much as you want.
GETTING READY
Once you enter with your electronic bracelet, you should head to the changing rooms. There are lockers you can simply keep your personal items safe while you enjoy your time. Before you change in to your swimming suit, you are expected to take a shower. In many blogs I read that people were complaining about the lack of privacy, but when I was there, the shower areas were private. You just should cover yourself with a towel and have your swimming suit in hand before you reach the shower cabin. Again, if you prefer to keep your hair dry, the shower cap will be useful.
After the shower, get your towel and head downstairs. You can go outside and jump to the warm water, but you can also take a left turn and use the "exit" sign to get in to the water before going out - so you will not have to suffer being without clothes outside under challenging weather conditions.

You can keep making photos, since it is not forbidden or anything, but the high percentage of minerals in the water prevent you to make underwater shots. Still, bring your water protection with you not to damage it from water drops or steam. Make sure that your camera doesn't get affected by the evaporation so your photos will come out clear and bright.
Enjoy!