Oracle Database - Alert Log / Diag Locations

How to quickly find out where are my alert log and other diagnostic information. 
Either you can go to Oracle Base and browse using logical nomenclature which is 

<$ORACLE_BASE>/rdbms/diag/<db_unique_name>/<inst_name>/

or you can directly find out using 

V$DIAG_INFO

set lines 500 pages 500
col value for a100
col name for a60 
select * from v$diag_info;