I visited this WHS in May 2017. It is definitely one of the best day trips from Seoul and one of the most impressive fortresses in South Korea, not only for its size and condition but also for the different military constructions and defense structures.
Being Spring meant that admission was once again free of charge. From the subway station in Suwon, we caught a standard taxi to Paldalmun Gate (bottom left photo), one of the 4 main gates of Hwaseong Fortress completed in 1795. It is one of 2 gates with a semicircular reinforced defense wall, quite similar to the Heunginjinmun Gate in Seoul. The only pity is that it is used as a very busy roundabout. There are several coffee shops with terraces for good photo opportunities.
Paldalmun Gate was our starting point to cover the whole 5.74km circuit on the fortress walls, stopping at intervals to take pictures and to explore the many exits which led to other paths beneath the walls or to other defense structures. We headed straight uphill for what was to be the longest stretch uphill of the whole circuit. After that it is a very pleasant walk with several panoramic viewpoints. There are 2 UNESCO WHS stone markers, just a bit further on after you climb from Paldalmun Gate, and another next to Hwaseomun Gate, where locals and tourists, young and old, enjoy kite running and archery. A section of the stone wall on the left of the Hwaseomun Gate contains the names of all those involved in its construction.
There were long stretches of the fortress walls where we were alone except for some black squirrels and passerine birds. My favourite defense structures apart from the gates, were Seonbukgongsimdon (Northwestern Watchtower - bottom right photo), the 7-arched Hwahongmun Flood Gate (top left photo) and the unique Bongdon Beacon Mound (top right photo) with 5 signal chimneys used in combination to send different messages. 1 was lit in normal times, the second was lit when the enemy was spotted close to the national border, the third was lit when the enemy reached the border, the fourth was lit when the enemy crossed the border and the fifth one was lit when fighting took place.
Overall, this is one of South Korea's best WHS and if you have enough time I'd even recommend staying overnight to see the fortress at night. Do try the local speciality - Suwon galbi :)