This is District XVII, on the edge of Budapest, near Ecser and the airport. However, instead of going to the flea market or taking off, here you can watch deer and foxes, and explore the very last remaining marshland of Budapest. Merzse, located in the Pest side of town, has a unique microclimate; during droughts, only the reeds and bulrushes indicate that you have arrived, but the area comes to life when there's a lot of rainfall. It's a great excursion spot all year round. After getting to know the hills and valleys of the Buda side, the marshland with all its birdsong and a 6-kilometer long study trail is a nice alternative. The peaceful nature reserve is a popular destination for school field trips and for taking dogs for a walk, and it is a notion among locals.
How to get there: Rákoskert train station is about a 20-minute train ride from Keleti Railway Station. Turn right from there and walk along Kísérő utca, until the railway crossing, then go straight across and you'll be at the winding forest trail. Signs will indicate the road from there.
Tip: Make sure to bring some insect repellent with you in the summer.