store tarn, christiansø

Ertholmen is a place steeped in history, a handful of islands, two of which are inhabited. They are the easternmost outpost of Denmark.
The first people to live here were soldiers, because in the 17th century Denmark needed a naval base and there was a natural harbour between Frederiksø and Christiansø. Today's ferry and lots of fishing boats and private yachts are still using it. Also a fort was built and extended over the years. In 1808, when Denmark was at war with England, an English armada tried to land but was driven away by cannon fire and bad weather. In the early 19th century there also was a political prison on Frederiksø for people who demanded more democracy. When the barracks were no longer needed, the Danish government allowed fishermen and former soldiers to live in the old buildings (the flats must be tiny but that's just a guess as I've never been inside one).
Some painters and birdwatchers also came, and these days the islands are a tourist attraction. Most of the houses are Listed Buildings, and the post office sells special stamps. They've even got a small inn where you can book rooms for a longer stay, but most visitors just come for a "day" trip (three hours) by ferry from Gudhjem. In the summer season there are three trips to the islands daily but you have to leave on the same boat that took you there, otherwise everybody would want to leave on the last one.
Store Tarn, the Great Tower, serves as a lighthouse and can be visited during the summer months. From the top you have a good view over the little archipelago. Sadly, on my two visits to the islands so far the tower was closed.
The pond is a rainwater cistern. Water is precious, so toilets are flushed with sea water, and the drinking water comes from such cisterns.