Credits

Many images are

3810883372_ef98b169d4_o.jpg http://www.flickr.com/photos/eprater/3810883372/
3810068953_6345698d9c_o.jpg http://www.flickr.com/photos/eprater/3810068953/
2481659776_00d90e90ae_o.jpg http://www.flickr.com/photos/chagiajose/2481659776/
1063195978_2d7f88d911_b.jpg http://www.flickr.com/photos/grisei/1063195978/
5630719398_4f3e829d67_o.jpg http://www.flickr.com/photos/morgner/5630719398/
3739735219_80c4d7f63f_o.jpg http://www.flickr.com/photos/43992178@N00/3739735219/
3782574160_1e33ce67fe_z.jpg http://www.flickr.com/photos/alexanderkirk/3782574160/
4421677863_40003906c3_o.jpg http://www.flickr.com/photos/dierkschaefer/4421677863/
5804519754_2bb5cd1a40_o.jpg http://www.flickr.com/photos/30478819@N08/5804519754/
5803964683_58371ce6ed_o.jpg http://www.flickr.com/photos/30478819@N08/5803964683/
5803963963_8220699a58_o.jpg http://www.flickr.com/photos/30478819@N08/5803963963/
3974210453_e2c8b52a2b_o (1).jpg http://www.flickr.com/photos/jenniferwoodardmaderazo/3974210453/in/photostream/
3974206429_34b09c92cc_o.jpg http://www.flickr.com/photos/jenniferwoodardmaderazo/3974206429/in/photostream/
3810917560_07b881eed1_o.jpg http://www.flickr.com/photos/eprater/3810917560/
3291806530_478884b5ac_o.jpg http://www.flickr.com/photos/mara_earthlight/3291806530/
5586817114_8d6fde2363_o.jpg http://www.flickr.com/photos/igorschwarzmann/5586817114/in/photostream/
4247603529_ae3ffdb8e3_b.jpg http://www.flickr.com/photos/sebastian-baryli/4247603529/
5216175028_4b68b52dc2_o.jpg http://www.flickr.com/photos/evocateur/5216175028/
6493344811_8e09aa04bb_o (1).jpg http://www.flickr.com/photos/mas_at/6493344811/
4192188481_1922911d4c_b.jpg http://www.flickr.com/photos/14174853@N04/4192188481/
1711544054_fa832eb02f_o.jpg http://www.flickr.com/photos/oksidor/1711544054/
1710693759_572cf08be3_o.jpg http://www.flickr.com/photos/oksidor/1710693759/
2164317950_37b386a7da_o.jpg http://www.flickr.com/photos/el_doctor/2164317950/

789px-Wien_Fillgraderstiege_Frontal.jpg http://en.wikipedia.org/wiki/File:Wien_Fillgraderstiege_Frontal.jpg

3823369801_62da387c94_o.jpg http://www.flickr.com/photos/borisvienna/3823369801/

4529128418_707b44dcf6_o.jpg http://www.flickr.com/photos/alfreddiem/4529128418/

Also many of the images are public domain and provided by Peter Gugerell, Vienna, see more of his work at https://commons.wikimedia.org/wiki/Category:Images_by_Peter_Gugerell,_Vienna