The Kastellet, Copenhagen's fortress that was built in the 1600s, is a wonderful spot to go for a stroll on a warm day. Admission to the grounds is free and the long walk on the ramparts provides great views. Some of the barrack buildings are open for tours and there is a small museum.

Its a nice old fortress still occupied by the Danish Army. There's not much to do and there are strict rules such as not touching the cannons but its a nice place to walk or run round in the morning and breaks up the journey from the metro to the mermaid statue. You could also dip in and wait for some cruise passengers to depart too!

It has to be one of the highlights of my Copenhagen trip. A spacious and beautiful island that sits in its own little spot yet attracts so much beauty and peace and tranquility. A brisk fun walk with gorgeous views and a centre town that is historic and still put into excellent use by the Danish armed forces.

A green area near the little mermaid with a lot of architecture of the former Citadel. A well conserved defense structure where you can walk around, still being used by the way. Lot to see here: historic mill, a monument in honour of...

Kastellet ("The Citadel") is one of the best preserved fortresses in Northern Europe. A number of buildings are located within the grounds, including the Citadel Church as well as a windmill. The Commander's House, which was built in 1725, served as the official residence of the Chief of Defence until 2008. The Rows are six two-storey terraces which were originally built by Henrik Ruise as barracks for the soldiers. The two storehouses also date from the foundation of the Citadel. The Citadel Church was built in 1703–4 during the reign of King Frederik IV. It includes sound holes to the prison to enable prisoners to follow services. A prison complex was built on the rear side of the church in 1725. Eye holes in the wall between the church and the prison cells made it possible for the prisoners to follow the church services. On the King's Bastion, in the southwestern corner of Kastellet, stands a windmill built in 1847. See our pics from another gorgeous weather day!

A lovely peaceful place to walk round the embankments and take in the views. So close to the little mermaid but most people probably don't visit. The walk round the embankments and seeing the windmill, church and barracks was more impressive than the mermaid to be honest and free.

If you are leaving your cruise ship and pass by what appears to be nice greenery and meandering rivers don't be fooled. Welcome to the Citadel. It seems nice and peaceful from the outside. However, you can walk through and get closer to the windmill, church, and what appear to be barracks. There are guards but you can pass through without screening. Nice to know what is on the other side of the moat.