Fortifications that consituted the Warsaw Fortress in the 19th century. Four of them were preserved, these are: Fort IV Chrzanów, Fort III Blizne (Groty), Fort IIA Radiowo (Babice), Fort P (Parysów) Bema.  (PDF, in Polish)
Transatlantic Radio Exchange (Transatlantycka Centrala Radiotelegraficzna), or rather ruins thereof  (in Polish). The twin object in Grimeton, Sweden is still preserved .