1. Show us your favourite picture of the Northern Line or a Northern Line station. It can be a picture you have taken or created yourself. Alternatively find something on the internet that sums up the Northern Line to you. Dmitri wanted to make it harder and get you to take your own picture, but I'm being a bit more generous here.
2. Tell us your favourite place that you can visit from the Northern Line. It can be a boozer in Burnt Oak, a watering hole in Waterloo or a hip place in Hampstead.
3. Let's say Ken Livingstone wants to increase the numbers of people travelling on the Northern Line. Can you help the Sheriff come up with a slogan or by-line or jingle to get people to travel on it? How about The Northern Line: Faster than a speeding snail?
Just one answer or suggestion for each section please.
Dmitri and I will put our favourites into Neil's paperclip selection and the overall winner gets Dmitri's prize of The Northern Line book. I'll probably throw in some more surprise gifts for the best entries in each section.
To enter leave your email address and/or blog/website with your answers in the comments below. Please leave all your answers in one entry and you can only enter once! You have until 23.59 GMT, Sunday 23rd July to enter.
Have fun and thanks to Dmitri for the prize and competition!