So, I need a reason for going into a dungeon

I already have a world map and knowledge and image of different locations, as has my player. We did launch our Dungeons & Dragons game yesterday, a bit like introduction.

Character arrived to town what is actually now made of four barricated tent supplements. At the south from these four tent compounds what are now called: Sumer Camp. Sumer Camp is located to the west for human capital Sword city in the Victory plains.

Before Sumer Camp, there was Sumer City. But it was raided by hobgoblins and people living there had to flee. They bledged help from King of Sword City, but king was not interested in sending army to protect that farther side. And there is a river separating Sumer City, so it has almost no value for Sword City.
Residents of Sumer City decided to fight back the hobgoblins who had taken their city and made it their own. But citizens of Sumer City couldn't attack, but they are strong enough for defence.
That is how Sumer Camp was found next to the city they had lost for horde of hobgoblins. They don't want to move away, are powerful enough to defend their camps and wait for a good opportunity to take their City back.

A: Sumer Camp tents are above each other. Northest is where common people live. Second north is guarded mediocre and there are some services as blacksmith, tavern and so on. Below that is military camp what mainly guards the Sumer City's borders. Just below Sumer Camps military camp is their main camp where the Chief of Sumer City/Camp lives.
Every tent is fortified with long logs cutted from the forest near to the south west.
B: Outside camp. This is temporary camp for travellers. It is quite safe, as hobgoblins mainly roam at behind Sumer City walls and at north west part of Victory Plains.

C: Sumer City. Northern of two cities is one where Chief had his moderate mansion as commoners did live. Souther is Sumer City's old military base now heavily guarded with hobgoblins who have no courage yet to attack Sumer Camp.

D: To the east from Sumer Camp is a hill where is old guard tower. It is manned by few Sumer guards. The view from the hill is good for every direction, and on the top of guard tower is a bell what is gonged in the sight of danger.

E: Old Sumer City fields and windmills. They aren't currently used because of hobgoblins which doesn't hesitate to attack workers and Sumer Camp cannot afford any of it's guards for the people in the fields.

Sumer Camp Services

Sumer Camp Guards

Sumer Camp Duke

Guard Tower

Fields

North-East of Victory Plains

Hobgoblins of Sumer City

GOTTA KEEP A BREAK! WILL CONTINUE LATER!