There are different tasks you have to perform to unlock the whole area, and there are also prizes. The Stronghold is located south of Edgeville, right above Barbarian Village. To enter, go to the west side of the building, and enter through the “Jail Entrance”:

When you enter, you will be taken to an underground jail, with 8 cells. Go to the north and you will see a guard, talk to him:

He will tell you that if you want to go to the training area, you must learn about player safety. So, you will have to read plaques on each cell to learn what the gublinches did wrong, and then you may enter.
First Plaque:
This cheeky gublinch claimed to be a Jagex Moderator! He was reported right away and dealt with.Second Plaque:
This wretched gublinch was asking a player for his telephone number. The player helped us catch him by refusing to give their information and reporting the gublinch straight away!Third Plaque:
This sly gublinch wanted to meet one of his player friends in the real world. The player obviously refused and reported him straight away.Fourth Plaque:
This vile gublinchette was asking a player for his home address. The clever player didn't give her their address, but used the Report Abuse button to report her instead.Fifth Plaque:
This evil gublinch asked a younger player where they went to school. The player was smart enough not to tell the gublinch and report him instead.Sixth Plaque:
This naughty gunblichette gave a player her email address. The wise player hit the Report Abuse button straight away, allowing us to catch her!
After reading all the plaques, go talk to the guard again. He will talk a little about the Report Abuse button, and you'll be on your way!
Now you will find yourself in a classroom upstairs. At the front of the class, Professor Henry will be waiting for you:

He will offer to give you a test about player security, take it. Here are the questions and correct answers:
Question 1:
A player has asked you for your personal details, including your phone number, home address and email address. What do you do?
Answers:
Give them my personal details
Say “No” or ignore them
Say “No” and ask for their details instead
Question 2:
A player that you do not know has sent you a private message that is offensive. What do you do?
Answers:
Nothing. I can't report anything that is said in private chat.
Send the player an offensive message back.
Use the Report Abuse button to report the player and add them to my ignore list.
Question 3:
Where should you go in order to read about playing RuneScape safely?
Answers:
There is nowhere to go.
To the "Safety & Security" section of the RuneScape homepage
Question 4:
You are approached in the game by a player named JagMod999. This player claims to be a member of Jagex and asks for your personal details. What should you do?
Answer:
Do not answer any questions and report the player using the Report Abuse button at the bottom of the game screen.
Give them all my details; they are a member of Jagex after all.
Question 5:
How long should you play RuneScape for any one time?
Answers:
As long as I like. I'm having fun and don't want to stop.
I should take regular breaks in order to stay healthy.
Question 6:
How do you report a player for breaking the Rules?
Answers:
By using the Report Abuse button at the bottom of my gaming screen.
I'm not a tell-tale., so I don't report players.
Find a Moderator and get them to report the player.
Question 7:
A player has started to ask yu personal questions that make you feel uncomfortable and you'd rather not answer. What should you do?
Answers:
Answer them anyway.
Do not answer any questions and report the player using the Report Abuse button at the bottom of my game screen.
Question 8:
You are asked for your full name and date of birth by a player that you have been chatting with for a short while. Should you give them these details?
Answers:
No. The player can use my information to steal my identity. I don't want anyone pretending to be me.
Yes. There's no harm in telling someone my full name and date of birth. Maybe they want to buy me a birthday present!
Question 9:
A friend you met playing RuneScape has asked to meet you in real life. What should you do?
Answers:
Meet them. They've been a friend in-game for a while now and they're really nice ... Say no and do not meet them.
Once you get all the questions right, this will appear:


Now talk to the professor and he will mark it. After it's been checked and it's all good, he will tell you this:

And Here is Your Reward:


Each lamp give you 500xp in any skill, so that's a total of 1000xp:

And Here is the New Emote:


After this, you can now enter the Stronghold through the outside doors, and not having to go through the jail entrance. Now on to the exciting part, the new dungeon! Go back downstairs to the jail. Look on the mini-map for the red exclamation mark, that's where the entrance is. You must “pull back” the poster:

Now you are in the dungeon! There are some new monsters here. This is a list of all the monsters there:
Level 6 Muggers

Level 8 Cockroach Drones

Level 56 Cockroach Workers

Level 83 Cockroach Soldiers

The dungeon is a bit confusing, with four floors, and different doors, levers and ropes. Walk around a bit to get used to it. O the first floor, go to the north-east corner and you'll find stairs, go up them. On this floor there is a lever, pull it:

This will unlock a door on the 1st floor:

Go through it and you'll be on the same floor, but a different section. Look around for this chest and open it:


You get 10k and safety gloves!

Now go back the the floor where you found the lever, and right beside it there is a string, climb it and you'll be on ground floor just where you started!
FAQs
- Where is the Stronghold located?
Like I mentioned above, north of Barbarian Village and south of Edgeville. - What songs are unlocked?
Incarceration, Safety in Numbers and Exam Conditions. - What's the point of this?
So you get to learn about player safety. - What are the rewards?
3 new songs, 2 500xp lamps, a new emote, and dungeon training area, 10k and safety gloves.